Hi Redrumloa:
if you REALLY have access and the option to do hardware, youmight start out with an already designed turbocard for the A500(+) / A1000 / A2000. You could sell them CPU-less, for a better price.
The German c't magazine has, in 1994, published the layout and all necessary things and documentation for a PAK, a ProZessor-Austausch-Karte, meaning "CPU-exchange-card". It offered up to an 68030@50, plus 68k-fallback mode and a kickstart-rom.
You can find some info here:
http://amiga.resource.cx/exp/search.pl?product=PAK&company=Even more interestingly, it offered the option of adding a small RAM-daughterboard for using SIMMs up to 64MB.
Considering how much accelerators bring on eBay these days (easily 125+ Euro), you might make a start there.
Tell me if youd like to contact the team of the c't, I can find you some email-addys.
McTrinsic