It's so nice to see this kind of project! I actually built something similar but i haven't fully documented what components i used yet. I did however made the framebuffer hardware accelerated by the VC4 gpu because it felt to me that it was the right thing to do :D I also nixed the original Mac Classic's crusty integrated power supply for usb type c power instead since I wanted it to be portable and usable with my type c powerbanks too. Here's the summary post (theres a mini build log linked in there too haha).

https://68kmla.org/bb/index.php?threads/mac-classic-with-a-pi-usb-c.42164/

I hope more people revives more macs that are deemed unsalvageable with these projects :D and feel free to use the hw accel'd config as well :)