lo-tech 1MB RAM card if you want modern, you can even buy the blank PCB and assemble it yourself if you're so inclined

it will round out your 640kB base as well as give you as many UMBs to play with as you have address space for, which is rad.

Only thing is the edge connector is not hard gold or beveled, so don't cycle it a bunch of times. You can cut the bevel yourself on a belt sander or bench grinder but the surface finish on the fingers is ENIG and will wear off eventually.

Thanks 😀 I’ll look that up. Yeah 1MB would be great but I at least need 640