Moldvay’s class descriptions (B9-B10) are wonderfully short, which allows one to focus on each class’ core characteristics. Some ground rules for converting to Chimera:
Advancement Cost (AdCost) is determined using the guidelines for Creating New Races and Classes (CB/9) 
Each class restriction in Moldvay is represented by a Flaw (CB/11), which reduces AdCost by -1
Since race equals class, I’m using the Variable Wound Limit guidelines to give PCs a fighting chance at survival:
Moldvay HD 1d4 = Wound Limit 1d4 (AdCost +1)
Moldvay HD 1d6 = Wound Limit 1d6 (AdCost +2)
Moldvay HD 1d8 = Wound Limit 1d8 (AdCost +3)
Sperks listed in the conversions below are outside Moldvay’s purview, but are included for your consideration. They are completely optional; PCs may choose some, all, or none with the provision that each Sperk selected increases AdCost by +1 (CB/6).
Characters are still created using the Chimera Character Generation guidelines (CB/5); just substitute steps 2 and 3 with the converted Moldvay class.
Moldvay describes clerics as “humans who have dedicated themselves to the service of a god or goddess.” (B9) They’re allowed to wear any armour, but cannot use edged weapons. Clerics can cast spells upon reaching 2nd level, and they can turn undead.
In my early days of playing D&D, I figured clerics were essentially priests. But there are a few clues to suggest otherwise. First, dedicating oneself to serving a god doesn’t require ordination—in other words, clerics don’t lead congregations, conduct worship services, or represent the church in secular matters. Second, clerics don’t get spells until they “have proven their devotion to their god or goddess,” which tells me that they’re being “tested” at 1st-level. (B9) Third, they’re martially-inclined, as opposed to experts in the more priestly pursuits of mythology, scripture, evangelism, and church bureaucracy.
It’s easy, then, to cast the Moldvay cleric as a holy warrior, essentially an elevated lay-person in a religious fighting order. Think of a Templar—certainly dedicated to the service of his god, but more as an instrument of the church than the religion itself. By implication, the actual priests of the campaign world are too busy tending to their congregations to do any adventuring. Thus, the cleric is the church’s representative in the dungeon, equipped with some fighting skill, good armour, decent weapon use, power over the undead , and (eventually) spell-casting ability.
Clerics are humans who serve the earthly interests of a specific religion, typically as members of a fighting order, though they can also act as missionaries, healers, and anchorites. As adventurers, they may wear any armour, but are restricted to non-edged weapons. All clerics have certain influence over the undead.
At 1st-level, clerics must prove themselves worthy of service within their order. Attainment of 2nd-level is sufficient proof, after which the cleric is given access to the the order’s lectionaries, thus acquiring knowledge of a single school of power. Because their spells’ source is divine, clerics do not have to learn individual powers: Once a school is known, the cleric may pray for any power within it. Powers are loosed normally, though clerics use the Mettle Ability instead of Wield.
Move Rate: 12”±1d6
Wound Limit: 1d6
Abilities: Fight, Mettle
Perks: Clerical Spells (access to 1 power school at 2nd-level), Turn Undead (see below)
Flaws: Restricted Weapons (non-edged only)
Special Perks (Sperks)
Clerical Spells: Required for each additional school of power known beyond that attained at 2nd-level
Divine Favour: Improve Resistance vs. 1 power school by level (usually the school accessed at 2nd-level)
Holy Roller: Increase attack ARs vs. the infidel by level
Pious: Roll 1d8 for mana (CB/13)
Unshakable Faith: Holy symbol not needed when attempting to turn undead
Weapon of God: Can use weapons espoused by religion (even if edged) to the exclusion of all others
Since this ability is usable at will, I’m equating it to the Improved Power adaptation (CB/21) for an AdCost of 2 points. To turn undead, the cleric brandishes his holy symbol and makes a Mettle roll against a Target Number of 8 plus the combined level of all undead affected, with the following results:
CF: The undead get angry; for the duration of the encounter, they gain +1 to (d6: 1 Movement Rate; 2-3 Fight rolls; 4-5 Damage rolls; 6 Wound Limit)
NF: The undead ignore the cleric
NS: The undead obey 1 order per level of the cleric, to the best of their ability (e.g., Halt, Flee, Drop your weapons and return to your resting place, etc.)
CS: The undead are Vanquished (CB/18)
Only one turn attempt per encounter is allowed, though the cleric may target any and all undead creatures within 10’ per level. The cleric may selectively target small groups or individual undead to make the attempt easier, but this counts as the turn attempt for that encounter.
Brother Pater (Mettle +2) encounters 2 skeletons and 3 zombies. His Mettle roll is against TN 16 (8 + 2 [2 1st-level skeletons] + 6 [3 2nd-level zombies]); he must roll a 14 or higher on his Action Roll to succeed.
I’m interested in your thoughts, particularly if you think the conversion above cleaves closely enough to the Moldvay version to retain the race-as-class feel of B/X. Or, put more securely, is this class more, less, or as playable as your basic old-school cleric?
Just to keep myself on the beam (and to give Chimera a fair challenge), I’m keeping Advancement Cost values in proportion to the Moldvay Experience Point (XP) requirements. To do so, I’ve divided the XP required for 2nd-level (B8) by 250 to get the base AdCost (rounding up).
I say “power over the undead” deliberately, as this has implications to setting design. In game terms, the ability to “turn undead” is a niche ability useful against a foe that typically defies mundane attacks—it is incentive to maintain a balanced party. Yet in campaign terms, it establishes the connection between faith and death, which is a common characteristic to most real-world religions. If man looks to the gods for answers, and the biggest question in life is about what happens when you die, it makes sense for the cleric to exert some influence on the undead.
Additional power schools may be available at the GM’s discretion, but require purchase of the Clerical Spell Special Perk. Tangentially speaking, I figure each god or goddess has access to power schools in accord with its sphere(s) of influence and in proportion to its standing in the immortal hierarchy. Naturally, the availability of spells to clerics is limited to those schools known by the deity served. By extension, the school acquired upon reaching 2nd-level would represent the most dominant school within the deity’s portfolio; access to other schools might require additional level advancement, special service, or perhaps be proscribed from clerics (but not priests) altogether. I have a table for this, but this is clearly a separate topic...
My target AdCost is 6 (1,500XP / 250 = 6).
Moldvay, Tom, ed. Dungeons & Dragons Basic Rulebook. Lake Geneva: TSR Hobbies, Inc. 1981.
Smale, Erin. Chimera Basic. Atlantic Highlands: The Welsh Piper. 2011.