There’s a nice C64 and Amiga compendium free available but only in German.
It’s written by Peter Sieg and he offers the complete book as pdf and odt under the Creative Commons license.

Find the book and all files (firmware, layouts, etc.) under the link below:
Commodore-Hardware-Retrocomputing. 25 Jahre nach C64 & Co.: C64 und A500 reparieren, warten und erweitern

Direct link to the github repository:
https://github.com/petersieg/Retro-Computing