New heat in the shop ..electric furnace help

Aluminum wiring????????

That could be bad news - especially in a high current installation like this. You may already know - the other critical thing about Al wiring and the Electric Code, is that you MUST use AL/Cu rated connectors.
WE have Al wiring in my house and I've had 1 near miss where the receptacle for the dryer overheated.
If it were me - replace the Al wiring with Cu now - before you have a fire. It is not worth the risk.
Not sure about your area- but up here, the insurance companies no longer insure houses with Al wiring unless Cu pigtails are installed at all connections.