1. Making Attacks (p 47 in Book of Adventure)
In the standard system, your chance of hitting an opponent is figured out the following way:
a) Consult the Combat matrix for different body types to get the base chance of attack. (Humanoid vs humanoid is 40% etc)
b) Compare Dexterity (modified by training) of the two attackers. Highest Dex gets a bonus to attacks. Lowest dex gets a penalty.
c) Chance of success may be reduced by opponents armor (Optional)
d) Chance of success may be modified by difference in size.
e) +1% per level
f) Roll below total on d%

Proposed House Rule:
Instead of starting with body types, I would use Dex (modified by training) as base chance of attack. From this number I would subtract the defenders Defense Rating determined by the following:

(Dexterity / 10) + Body type bonus + armor bonus

Very large creatures may get a penality to Defense Rating, while very small creatures may get a bonus.

2. Damage (p 49 in Book of Adventure)
In the standard system, damage is 1d6 (same as OD&D). There is an optional system for variable damage, but as this introduces a second dice roll and a chart to be consulted I don't like it much.

Proposed House Rule: Use weapon damage ratings from D&D/AD&D. Target body type may reduce damage (see armor below).

3. Strength Bonus to damage (p 53 in Book of Adventure)
This is an optional rule in the standard system. Characters with high strength get to double damage, while characters of low strength only get to roll half damage.

Proposed house rule:

Damage Bonus = Str / 10 (Modified by training)


4. Armor (p 52 in Book of Adventure)
Effects of armor are described as optional in the system. Armor both reduces your chance to be hit and damage suffered.

Proposed House Rule: As per house rule for "1. Making attacks" above, armor now adds to the defenders Defense Rating. Armor should also reduce damage, but I prefer a set number to the % given in the official books. Here is a proposed list:

Armor (Defense Rating / Damage Reduction)
Shield +10%
Leather +10% / 2
Chain + 20 % /5
Plate + 30% / 8

The numbers here may be subject to change. Certain body types (such as scales) may also get bonuses here, but I will get back to that.

These are just initial ideas and obviously have not been playtested. Thoughts?

-Havard

I am digging what I'm reading on these combat house rules!

I think the move away from body type and using DEX for basic strike chances is a great idea. Maybe body type could be a penalty or bonus modifier?

Maybe the basic game could be d6 weapon damage & the advanced could be variable damage?

The damage modifier you suggest is clear and simple to implement.

I don't see where armor is reducing the chance to hit in the RAW. They work as a separate roll, only affecting damage.