Last device on the end of the bus should also supply termination power. Internal device and the last device (as in the way they are physically connected to the bus, not to be confused with SCSI ID; ID of internal drive typically are set to zero) on the external bus should be terminated.

See if you can boot from floppy and run disk utils to see if the drives show up. I am inclined to think it's a driver problem; Apple as a company has serious mental issues when it comes to third party hardware, particularly during the 68k days.