I'm kinda at a standstill... but it's pretty simple for the most part.
Just gut your stuff and build a PC inside the cab. Then get MAME and find a frontend you like to run on boot.
A difficult part is using an arcade monitor as your display, I think there are GPUs that can work with these, but the whole 15 Hz thing kinda messes stuff up so you need to verify compatibility.
Controls are simple, best thing I can recommend is a KeyWiz or equivalent.
I like the KeyWiz in particular because it is PS/2. Works just like a standard keyboard. So just pick one that works for you, wire up the controls in a standard daisy chain, give the chip power and ground, and you're good to go.