Valkyr, the FED won't likely fit into the ZorkiC. You'd need another FED to do that. There are minor variations in the body shell stamping and other internal parts which prevents cross-transplants.
For the shutter, you could get a new set of straps and blinds. It is not good to use an old shutter from an equally old camera. It will likely break soon and be reason for another disassembly.
Speaking of FED repairs, I have 6 FED-1 bodies which I am in the process of repairing now. One FED, a prewar with 6-digit serial number, is missing a winding knob. Its original had its gears badly stripped. Another FED is missing its pressure plate. The FED pressure plates are perfectly round, unlike the 'band-aid' shapes found in Zorki (although the first Zorki also had round PPs).
Wolves: a semi-transparent mirror (50R/50T) could be ordered from Edmunds scientific. You can cut one to size - approx 8x10mm - and fit this in your FED's RF. The mirror need not be exact in specs as the original, as long as it fits into the RF box, it should work.
Jay