OK. You might never be able to boot off the PC disk to get the PC hard disk to get going, but you should be able to get access to the data. Very good chance of it.
One complication with the older drives - because they have multiple data cables, it is ever easier for just one end to be the wrong way around and the connections get scrambled.
You really want to power off and read a manual for the PC hard drive controller if you can. Make sure the cables are all connected correct way around, these older ones are tricky sometimes.
The reason you can usually do it from the Amiga side if you can suss out the controller is - you can usually get the PC going enough from floppy to mount the drive to DOS at least. That's one starting place.
This is not a SCSI or IDE drive, but if the drive spins at least, good chance you can pull the data from it, however it was setup to read to..
How good you can get Janus going to mount the PC hard drive from the Amiga is just a question of getting the right components, after that, should access OK. Sounds like it. One attempt if the circuitry on the drive has died is to try to find an identical circuit board, that can be swap out replaced on most types. Spinning drive healthy or savable mostly..
One very handy thing to know about working with old PCs. Digital Research DOS. It's very handy if you need a boot disk that will get you to a DOS prompt on a real PC. Works usually on emulators too, but you want about 5.31, not much later if any. DOS is DOS nearly 100% on these early PCs. You don't have to touch microsoft products to do it, but that's another way.