Well, since Commodore never released a "combined" Kickstart+Workbench disk, it's pretty obvious that you're dealing with a system that's been modified by a previous owner. Possibly heavily so. It's possible that the disk contains just enough logic to get the system booted and then hand off the rest of the boot process to an external hard drive. A screenshot of the S:Startup-Sequence on the disk might yield some clues.
In any case, IMHO a thorough inspection (and probably a good cleaning) of the internals of the system should be your first step. Photograph and document everything you see that looks out of the ordinary. Then try to get it booting with standard Kickstart and Workbench disks. If you can get it going that far, then you can try re-adding some of that additional hardware you found.
Sounds like a fun project, keep us posted!
