As a 'B' model it should have the built in SCSI CD-ROM drive you can use to boot the reinstall CD, so if the missing SCSI HD is the only issue all you need to do is burn a copy of the A.02.90 reinstall CD, and obtain a SCSI HD to replace the missing one to install as a boot HD.
50-pin SCSI HDs are hard to find and expensive now. I use 68-pin SCSI HDs with 68-pin male to 50-pin male adapter plugs. Agilent also did that as original equipment at some point during the product cycle.
I've had OK luck using 68-pin IBM DNES-309170 9GB drives, although they can be a bit loud. I've never tried to fit an 80-pin SCSI drive and adapter to the 50-pin cable. That might be more of a mechanical challenge.