@Cyberus:
;-) Drivers for your GVP Impact! series II controller can be found at
http://www.L8R.net/install, if you need them. They may also have documentation for it, as well.
That site has gone to the trouble of obtaining permission from the respective copyright holders, so the software they host is legal, and free. They specialize in drivers for obsolete hardware.
:-( As for putting a new hard drive into the unit, be aware that Workbench versions from the late eighties used 32-bit addressing, and are thus limited to hard drives of 4 Gigabytes and smaller, with partitions limited to 2 gigs for most directory utilities. It's a file system issue.
;-) Later versions of Workbench (3.5, 3.9), and some of the filesystems found on Aminet, however, don't share this limitation. Armed with one of these, you should be able to use any sized SCSI drive you can find. And, yes, it's a 50-pin unit, so they're kind of rare, now. Try locating a computer recycling center near you. They may have them cheap.