At CBM engineer Bil Herd's website, he has released the drawings/blueprints for a proposed CP/M cartridge for the VIC-40. The cartridge would have used a Z80 chip. To read about it and to download the drawings, go to
http://c128.com/cpm-z80-cartridge-commodore-vic-40
Also at C128.com, he has released the schematics for a proposed C64 80-column adapter board which never saw the light of day. To read about it and to download the drawings, go to
http://c128.com/commodore-c64-80-column-adapter
He has released the schematics for the TED series (Plus/4, C16, etc.). To read about it and to download the drawings, go to
http://c128.com/ted-drawings-1980s
Sign up for his forum, and you could directly ask your questions to Bil.
Truly,
Robert Bernardo
Fresno Commodore User Group
http://videocam.net.au/fcug
The Other Group of Amigoids
http://www.calweb.com/~rabel1/
Southern California Commodore & Amiga Network
http://www.sccaners.org