I've never really gotten much chance to use d12s. It's a shame, really. They're like low-resolution d20s, nice and round and chunky to roll.
d10s are dumb. Too pointy. Anyway.
So, what if I wanted to redo all the ACKS skills and proficiencies in d12?
Spreadsheet. (Google! Y U No let me cut+paste from your apps?)
To read this, say you need an 18+ in ACKS. That goes closest with 2:12 - you've got a 1.67% better chance at 2:12 than 18+. Our biggest flux is +/- 3.33% - that's less than a +/- 1 on a d20, in theory.
I expect this to all fall apart on the next table. Let's see what the thief skills look like. We'll start with Open Locks.
OK. So, 'Diff' is the percentage change from X+ to X:12. Some levels fare better than others. 'Delta', however, is the change in change from one level to the next - a level 1 thief in X+ gains 5% more ability when she hits level 2, in X:12, none - she loses 5%, essentially, from her guildmate using the X+ system.
Lucky level 7 is the best it gets.
Worth doing? Probably not. ASSH actually uses the venerable d12, whereas I'd be hard pressed to place the die in anything ACKS does.
It's much better systemically to follow along with ACKS using a d20 than to introduce Yet Another Wrinkle in what to roll for what.