I’ve been working on a mod to upgrade my 512K (which has 512Ke ROMs, disk drive, and an 1980s aftermarket SCSI adapter) to 4MB. I tried breadboarding it, but of course that didn’t work, and it’s a total nightmare to troubleshoot. I’m now planning on going straight to laying out a PCB to prototype it instead. In fact, I’d really like someone else with decent knowledge of Mac memory addressing to review my schematic before I go through all the trouble.
I’ll start my own thread and link to it back here.