I'm afraid changing the mask and the size of the transfer really doesn't matter; I won't cite references but I did an extensive search recently and found this to be an "old wives tale.". The CSPPC SCSI (cybppc.device) is a 68-pin UWSCSI bus supporting 15 devices with up to 8 logical units and one controller defaulted to #7; unlike the Blizzard SCSI device that HAS internal termination, the CSPPC needs two (2) "Active, Wide, LVD/SE powered terminators." These correct for signal irregularities at UW speeds. Without them you are prone to hobgoblin of bus errors -- odd, irregular, unpredictable errors. On top of that, the SCSI controller does not play nice with a bunch of hard drives. It also does not like having U160 and U320 HDDs on the same bus.
The bus should look like: TERM---CSPPC---Drive---Drive---TERM.
Look on EBay or the Internet for "female, active, wide, LVD or SE 68-pin terminators." They run about 5 to 10 US, not 40 to 60 US.
The truth is out there, just search for it (and take notes).