Howdy, the GVP 3001 '030at50Mhz I have has no IDE. It has internal & external SCSI connectors. So I wonder why you need another SCSI card. From the different faults you have listed, and that it works without the Combo card, I might check the power supply. Whenever we would get non-consistent faults from a box, it would frequently turn out to be the P.S. as the "ripple" voltage was high enough to toggle bits.
Just a thought,