After Frankensteining two SA-801R drives (one picked up on eBay plus my own), I was able to get a working second drive. So, now, I have a good dual-drive setup for my IMSAI. I played a little Colossal Cave tonight.
I'm now on the hunt for a spare logic board. Mine is an LSI-type, number 25229.1 (with a sub-number of 1952) with the LSI perpendicular to the edge connector (i.e., front-to-back when oriented on the drive).
So, if anyone has a flakey drive with a good logic board and is looking to get rid of it, please let me know.
Collector of Classic Computers
Build Master and lead engineer, Altair32 Emulator