Not an expert here, but what kind of monitor do you have, and what resolution are you running it at?
You might be able to force MAME to the resolution he set it for. If you're running a multisync monitor at 640x480 and he tweaked for 336x240, going back to something close to his tweaking resolution might make the settings fall right in line.
Does your monitor have a remote board so you can see the effect of the settings? If not, you could put a mirror in front of the cab where you can see it and just move the knobs slowly. Its a pain to keep going from the back to the front of the cabinet, and easy to miss the effects of the changes you made unless they're drastic.
Make notes as you do this, because it will simplify things if you ever have to do it again.
