In the previous post I mentioned using Target 20 and Homebrew Homunculus’s simple d20 skill system. I should probably also mention that although I use those basic KéK classes, I did stick with Swords & Wizardry’s unified saving throw. Between the three of them those cover all the “core mechanics” in the game.
I arrived at Target 20 mostly through a process of elimination. I knew I did not want to do any lookups during gameplay so the traditional attack matrices were out. The logical alternative baked into S&W and also WBFMAG is ascending armor class. However, as HH has pointed out, S&W’s base ascending armor class of 10 is mathematically incorrect. You don’t really notice it when you use it out of the box, but I ran into trouble when I tried to come up with a player-facing defense roll that would be mathematically identical to a referee-facing monster attack roll.
This left me with two options: adjust the AACs listed in CX on the fly by 1 point (violating my rule to remain fully compatible with the module), or use descending AC after all. This is when the appeal of Target 20 really became apparent to me. It is both 100% mathematically identical to the original game, and very easy to use at the table. You just need to get over the fact that lower ACs are better.
Incidentally, it is also trivial to rewrite Target 20 as a player-facing defense roll:
Defend: d20 + your armor bonus + opponent attack value + modifiers ≥ 20
Armour bonus: 9 - AC
Attack value: 9 - HD
However, after using this for one session, I came to the conclusion that rolling to attack as a referee is actually faster (and possibly more fun). I’d gotten so used to The Black Hack’s player-facing defense rolls that I thought they were essential to a smooth-flowing game. But the big difference is that attack and defense rolls in TBH are exactly the same procedure, so there is no extra learning involved for players. With my so-called clever defense roll, players now need to learn two procedures. That’s one too many.
This is getting long-ish so I will leave discussion of saves and skill checks to future posts. I’ll just reiterate that Target 20 is indeed the superior procedure for attack rolls in classic D&D. I recommend using it.