To work with GSOS your card should be a Rev C. If there’s an original sticker on the EPROM, it should read

341-0112A for Rev A

341-0112B for Rev B

341-0437-A for Rev C

Or if the EPROM is a 2764 then it’s a Rev A or B. A 27128 and it should be a Rev C

The Jumper on the card is normally on the right set of pins.

You could try reseating the socketed chips on the card. Pry them up a little with a small screwdriver or knife and press them back down. That’s to restore contact in cases where the legs have a bit of oxidation.

You’re letting the drive fully spin up before starting the IIgs?

Have you tried changing the drives SCSI ID?