You could roll 2d6 and add bonuses to roll over a target, much like the Target 3:18 or Target 4:20 methods I described in the last post. The problem here would be that you'd have to set the target above the maximum roll to keep the probabilities close to the original. Target 3:18 is easy to remember because 18 is the max result on three dice, and Target 4:20 uses 20, the same target number as Target 20 or a critical hit in many d20 variants, but the target for 2d6 roll high over fixed target should probably be 13, which is not as memorable.
On the other hand, you could change the way armor is described and merge the attack roll with the reaction roll/turn undead mechanics. A Good reaction is a 9+ on 2d6. If you say, "you need a Good or better roll to turn undead of equal power or to damage an enemy in basic armor (leather and shield,)" then you can drop armor class and set these cumulative modifiers:
- Shield, No Armor -2
- No Shield -1
- Metal Armor +2 (double for Heavy)
That's not too hard to remember.
Of course, you could stick to the ACs as written and roll under AC. This is very easy to remember, but it does shift the probabilities a lot. Light or no armor becomes a bit easier to hit, plate becomes a lot harder. But I'm wondering if that might actually be desirable, to make unarmored combat much more deadly and full armor much more significant. I imagine those concerned about the balance of fighter vs. magic-user would especially love this, if the "no spells while wearing armor" rule is strictly enforced.
The bigger problem with all of these is that a 1-point bonus per level seems a bit extreme. You might have to switch to a "1-point bonus if attacker is a higher level than defender" rule instead.