BTW, who made that drive and what are specs? That looks a little beastly to be a modern drive ...
I think some of the last 320Mbs drives won't work at 20/40 without jumper settings (or at all). Some drives have a SE jumper you need to mess with. Most of the later drives are for servers and are SCA, you need a SCA to 50 pin adapter with a special terminator (SCA drives have no built in termination) to work in 8 bit mode on old macs.
Something like this: http://www.cs-electronics.com/images-large/ADP-9012.jpg
Or this: http://www.geeks.com/imageshare/S/300x300/SCATOSCSI-TERM-unit.jpg
It works well, I have some 9.1gb and 36gb drives in some older Macintosh computers, that's the good thing about SCSI, I haven't met a drive yet that wont "clock down" to the slowest SCSI bus. Makes up for how much of a pain in the rear it can be to get the right termination settings sometimes, lol.
DX and MonoPrice both have some good prices on the 68 <> 50pin adapters:
68M <> 50M (DX) (plug your 50pin cable into a 68pin drive)
68F <> 50F (DX) (plug your 68pin cable into a 50pin SCSI card)
68M <> 50M (monoprice)
68F <> 50F (monoprice)
Make sure those adapters have "upper byte termination". Some of them don't and cause headaches beyond belief. To use a 68pin drive in a Mac, I had to get an upper byte terminated adapter, plus add an additional active SCSI terminator to the end of the chain (Apple CD-ROM drives make lousy bus terminators).