Inside Macintosh is always a good read. It reminds me of the venerable old Commodore 64 Programmer's Reference Guide.
I have a copy of CodeWriter with all the A-line traps in it too.

Click to expand...

I find it difficult to follow in detail without a good background in Pascal. While I have been proficient in C in the past, I never learned Pascal.

So the progression starts to look something like:

1) Want to build an expansion card for an old Mac.

2) Gots to learn the stuff in Inside Macintosh in order to write the firmware and even to know how to configure the hardware so that it addresses the correct bits, provides meaningful services, responds to the system properly, etc.

3) Must first learn Pascal in order to understand Inside Macintosh....

Daunting.