Thanks for all the advice, unfortunately it took longer than expected to pick up the replacement logic board.

Long story short, after replacing the board, the original hard drive still didn't spin up - but a replacement drive worked fine. Now up and running System 7. It also boots fine off a Zip 100 disk (external SCSI) that had a backup of the original 80MB drive on it.

So I'm of the very inexpert opinion that both the original drive and some board component(s) were problems - perhaps one electrically damaged the other?

If I get the time, might be curious to see if a wash rejuvenates the old board, etc. Also wondering if this setup (IIsi Sys 7) supports larger drives (maybe 0.5, 1, or 2 GB SCSI) which seem easier to find.

Thanks again. Very much appreciated.