Reading a Mac IICi and SE hard drive on another computer
Since the old drives aren't spinning up, don't worry about the SCSI card, data cable, or jumper settings; all they should need to spin up is power (i.e. that 4-pin connector). Since the 50MB drive is working off the G4's power connection, I'm pretty sure that's OK... Which leaves problems with the drives themselves.

Many of those older drives were prone to stiction and similar problems. Essentially, the main spindle and platters would get stuck in place, and the spindle motor wasn't strong enough to spin it up. There were a variety of tricks for breaking them free, most of which involved some risk of damaging the drive beyond repair (like tapping the drive juuuuust so, or opening the mechanism and forcing the spindle "by hand").

Probably the safest thing to try would be refrigerating the drives (be sure to keep them dry -- no condensation!), then spinning them up cold. I had the most luck with spinning the drive in my hand -- the trick here is that you want to spin it flat, that is, spin it around the axis of rotation of the platters. If you're having trouble picturing what I'm talking about, don't do it, because spinning it on the wrong axis could easily make things worse. Actually, even spinning it on the right axis could make things worse; I make no promises at all.

It might also help if you can figure out the manufacturer of the other drive. If it's a MiniScribe 8425SA, I recommend a stake through the heart.