There's a PDF there of Programming The PET/CBM, by Raeto West. I loved that book - read it from cover to cover, drained it of all its knowledge. I can still tell you random things about the CBM-8032's memory map and ROM code, twenty five years after the last time I touched one.

I looked up Ray West recently, wondering if he's still alive. Turned out he was until recently, but he'd turned into a mad, racist, tinfoil-hat-wearing crackpot, paranoid about Jewish conspiracies and government hoaxes. Fluoride, fake moon landings, the whole nine yards. So sad. That guy was my hero, and he just went off the rails and, as far as I could ever find, completely disappeared.

ETA: nope, he's still around, and still antisemitic. Ah well.