Now, if it were me, I wouldn't run those rules precisely as published, but I'd attach a few well-considered house rules. Fortunately, there's not much work to do: my Original Edition Delta house rules, although written with OD&D in mind, are perfectly suitable for the exact same purpose in the case of Moldvay. In fact, in several cases, my house rules are actually more compatible with Moldvay than they are with OD&D Vol-1, because: (a) we both incorporate selected parts of the OD&D Greyhawk supplement, and (b) we both agree on the necessity of certain edits to matters of scale & time. (Remember: you can download the OED house rules for free from the OEDGames.com website, as shown in the sidebar here.)
I recently dug out my very beaten-up copy of the Moldvay Basic D&D rules just to check in on where we agree and disagree on the best practices for the game. Here's a "Top 5" list of stuff that we agree on as needing to be changed from OD&D:
- Class hit dice are as given in the Greyhawk supplement (Fighters get 1d8 every level, and Magic-Users get 1d4 every level; although I differ in giving Thieves 1d6 per level).
- Variable weapon damage from the Greyhawk supplement is used, but we both strip out the complicating "L-size" category of damage.
- Experience awards from monsters are given by a geometric scale, also taken from the Greyhawk supplement (in the past I used the linear system in Vol-1, but I've since been convinced that Greyhawk really is better).
- Miniature combat scale of 1"=5' is seen as necessary (Moldvay p. 61), as opposed to OD&D's 1"=10' or AD&D's often-forgotten 1"=3⅓' scale.
- Time scale really should be 1 round = 10 seconds (Moldvay p. 15, 23), as opposed to OD&D or AD&D's nutty assertion that 1 round = 1 minute.
- Class & race will be separate considerations, as in OD&D/AD&D; and clerics will be deleted, as usual for me. This leaves only the class tables for Fighters, Thieves, and Magic-Users. Elves will split their XP between the Fighter and Magic-User classes (and I do this by having them select one of those classes to get the XP before an adventure begins).
- I don't give the ±3 modifier at ability scores of 3 or 18, which Moldvay introduced. My feeling is (a) that's frankly too large a bonus for the scale of the system, and (b) it's better to have a pattern that you can continually scale upwards, i.e.: 13-15 is +1, 16-18 is +2, 19-21 is +3, 22-24 is +4, etc.
- Money will be according to a silver standard; encumbrance is tracked in stone units; and attack resolution is done by the no-lookups-necessary "Target 20" system (roll d20+level+AC >= 20; see the sidebar).
- Spell durations I measure as if 1 turn = 1 minute (same as the original Chainmail turn scale), not by the 1 turn = 10 minutes rule established in OD&D Vol-3 and carried throughout the rest of the Basic and AD&D lines.
- Monster hit dice and damage will all be 6-sided (as it was in OD&D pre-Greyhawk; so much simpler for the DM to roll!)