Yes, the hub brand and model should be stamped on the arm. It is most likely a CCM Hercules 37 or CCM Hercules 64, though they did sometimes offer upgrades to other makes. Once we know the make and model we may be able to come up with the missing part. Do you know what part it is? If not, we'll need a pic of the disassembled hub, so we can determine what's missing.

While I may or may not be able to help you out with the part, I can at least narrow down the model year of the bicycle, if you post the serial number