From what I read the SCSI2SD needs to be configured for the correct SD card size. The default is 2GB. This would explain why the partition which crosses the limit is not mounted.
gvpscsi and FFS shouldn't have any limits except the usual 4GB.
FFS of WB 3.1 works on Kick 1.3, so yes, you can use DOS\3. But you get an additional ghost icon for each partition.
