[throwanem]

It would have to vary pretty heavily by film camera model, and many probably can't be nondestructively modified that way. Nikon F and whatever Canon's film flagships were, sure - those are designed to take a motor drive winder, so you can remove the back cover entirely. But my heirloom Nikkormat FTn, for example, wasn't designed that way, and removing the film cover hinge pin would at best be a very fiddly task with a significant risk of damaging the hinge.

That said, and assuming you use a camera module that you can disassemble far enough to expose the sensor, it shouldn't be too hard. You'd most easily I think design and 3D-print a replacement cover with a light-tight fitting to place the sensor on center at the flange focal distance (ie in the designed film plane), and route whatever cables out to where you could connect them. Maybe also a case for the Pi that has a 1/4"-20 screw to mount on the tripod socket, just so you don't have to cram your face past it to get a good look down the viewfinder.

You'd probably have a hard time getting anything like a wide-angle shot. I don't know offhand what sensor sizes are common in RPi camera modules, but I feel like expecting 1"-class would be expecting too much, so you'd be dealing with a pretty fierce crop factor.