I honestly don't see the need to convert an old cab into a MAME cab...Restorations heck ya I am all for them...but for your own MAME cab why not just scratch build it?
Because some of us are much better at computer work than carpentry, or don't have the workship resources to handle 4x8 sheets of MDF. I know that I persobally fit into both categories.
I was fortunate though... I managed to get a cabinet that was begging to be MAMEd... a generic Konami cabinet that had been converted who knows how many times, had a plain control panel with 2 sticks and 14 buttons and clear bezel glass with no electronics.
However, there are many many times where I have found myself wishing the cabinet was just an inch or two wider, and that is the big plus of rolling your own... fewer compromises.
I have considered tearing apart my cabinet and just keeping the two sides and rebuilding it a few inches wider... the sides are the difficult part without a shop, tools or skills, the rest is just rectangles. I might be able to handle rectangles.