Good news. Bridgeboards are the most supported Commodore products, probably.
You are about to experience having two separate computer systems under the same hardware simultaneously, and both independently, and in a new mode, called harmony. This will be a new experience for you, although there are many variations of this and other multiple approach.
You need to run Janus software on the Amiga with all cards plugged in to the Amiga side and operating OK.
Janus does the bridgeboard bit. The hard drive almost certainly contains an image of an ancient PC that might be resurrected to full capability, which on a 386 running DOS, ain't a lot.
I hope you can cope with that barebones infomration and search Aminet for appropriate information and the local scrapyards for suiitable extra hardware to add.
At some point you will stop in this endeavour, that's cool. Janus could look forwards and backwards in time, mythology wise.
DOS Driver for that SCSI Card
Er, no. You got to have a compatible PC SCSI card that it was formatted with, sometimes. You can try with the SCSI controller you have, but PCs didn't have an equivalent to RDB at the time that was consistent across all systems. Depends when the drive was written, what with. Usually it changed with a manufacturer at least.
Even having the correct driver for what you have doesn't work sometimes, but strangely, having the right DOS driver for the partition, if the controller cards have same controller chips, can do the job. Filesystem issue with what the drive was written with. PCs had this problem. If the SCSI was done on the Amiga side, all will be well. If it was done PC side, that can be a huge issue.
Drive ST-506 possibly. Neither SCSI nor IDE.