xerox 820-II boot disk

You shouldn't need a lot of additional space. The adapter consists of a 50-pin edge card connector (you can make this from a cut-down ISA connector if you need), and the 34-pin connector salvaged from an old 5.25" drive PCB. If your PC doesn't have one, you will also need a PC floppy cable with a 5.25" drive connector. If you prefer, you could make the adapter using a pin-header and connect directly to a 3.5" floppy cable. You already have the 8" drives in an enclosure with power supply. You pop the cover off, sit your PC beside it with it's cover off, and run the floppy cable from the PC to one of the 8" drives. Trickiest part is iirc the 820 has single-density on the system tracks and many PCs can't do that. Depending on where you are located, there may be someone nearby with an 8" <> PC setup who can make you the disk. (Where are you?)