The SCSI standard uses a separate earth for every signal lead, to help enhance the screening and keep cross-talk down. The 25-way D-connector simply runs all 25 earth leads into one connection. You should be able to find somewhere, I don't know where offhand, an adapter to convert that to 50-way.
Apple used 25-way connectors, and so does my SCSI I/II PC ISA interface card which came with a SCSI scanner. That uses a 25-way D plug on one end of the cable and a 50-way Centronics style plug on the other end to connect to the standard SCSI interface on the scanner. It sounds like you might need something similar, but with a 50-way IDE style connector on the other end.
You might, again I don't know offhand, find a set of pins or solder pads on the Blizzard card that could be used for direct 50-way ribbon cable connection for internal use.