Listen here Purple Rain...

I have modified several curbside cabs for MAME installation, and I will tell you, it is probably more of a pain in the ass to modify and refurb a beater cab than to build one from scratch.
If you chop an old existing cab, you have several things you have to worry about:
Patching up any existing damage to the cab
Chopping cleanly... can't just take a chainsaw and go at it... got to be strategic about it.
Rebuilding the chopped up cab for structural integrity and asthetics.
Installing the monitor
Fitting a bezel around the monitor cleanly
Building a custom control panel (I assume this will be a MAME setup, therefore you would want a Frankenpanel because of your space limitations)
If you start from scratch, you have the pleasure of designing it according to your needs. Plus you won't have to worry about patching up any damage, and you won't be limited by the existing design of an old cab.
Either way, it is still a LOT of work to build or to modify a cab, so if you are going to put the work into it, might as well end up with something perfect for YOU.
Really, it will not save you very much time or labor unless you have modified several similar cabs already. I know this guy who MAMEs Midway cabs, and he has it down to a science. But he does them the same configuration everytime, and he has done a lot of them, so he can crank them out quickly. Every cab I modify is different and presents its own set of challenges, so it takes me a long time to finish each one.
Believe me, you will be happier with a scratch-built one.
