D2D,
The SCSI "standard" has been with us for about 12 to 15 years, and was a great idea. You could "daisy-chain up to 7 peripherals (hard drives, scanners, 12" writable ROMs, etc) on it and just give each one a different address.
Unfortunately, everyone had their own "interpretation" of it, and very often one device would not work with a given SCSI adapter (even before the advent of SCSI2 and later variants) and I have seen computers where 2 SCSI cards had to be installed for 2 SCSI peripherals - and both were a headache to set up!
I know it's not logical, but unless your old scanner has "wonderful powers" (like A3 scanning or incredible resolution) it will be cheaper to buy a new scanner (prices are way down these days) than to buy a new SCSI adapter card, and you eliminate the headaches of trying to get your scanner to work with the SCSI card that you buy.
Unless of course there's someone out there with exactly the same configuration who has done it and got it working . . . ?