I swapped the SCSI cable and it booted right up.

However, when I restarted it, it crashed at the Welcome to Macintosh screen.

I can get it to boot at random times.  Not entirely sure what's going on when it does successfully boot.

(It is is crazy fast when it does, though.  Maybe 8 seconds to boot the 512k to System 2.1.  Pretty insane.)