Woohoo! I terminated the wide SCSI on the back of the card, put the SIP terminator back in the first block, then connected my HDD to the 50 pin. No more 5 minute pauses! It still pauses, but only 3 or 4 seconds at those pause points instead of the 5 minutes. So it was definitely a termination issue.

Thanks for the help! I now have a working Jackhammer SCSI card.

Wouldn't mind knowing if I can use the new SIPs I bought, though, just so I have a full set of terminators and can change the configuration.

I might have a 68 pin SCSI drive in a box somewhere. Gonna see if I can fish it out.