Fascinating to think about the logistics with avoiding ROM – model compatiblity must've been a PITA! I'm even thinking about how to identify models – I know there's a pre-Gestalt Toolbox routine that doesn't need any Toolboxes, I guess?

Interesting.. I have some experience with the macintosh ROM from trying to fix up the EMILE bootloader for Linux (its boots like grub instead of being a macos app). Getting a recent GCC etc not to mess up calling stuff in the ROM was painful but QEMU emulates enough of the Quadra 800 that I could at least debug when registers were getting trashed etc with GDB. Alas, it still has some weird issues on real machines and randomly refuses to boot.

I'm going to do a u-boot port for the Mac at some point. It'll use the ROM to get loaded and then get rid of it. That'll work on nommu and mmu Macs and make the modern linux on Mac experience a bit nicer.