On 1955-59 Chevy/GMC, their optional deluxe fresh-air heater had mounting spacers. These fit around the seven attaching threaded studs that secure it to the firewall. Yes, the heater will mount and operate without them, but GM knew they should be in place. There are 5 spacers at 5/8” length and 1 spacer at 1” length.
These spacers assured the two large heater parts would be in a level position plus would have air flow behind them. These photos show a heater off the truck with their spacers around the threaded studs.
If your heater has lost its spacers over the year, a set is available from Jim Carter Truck Parts as part # MEH157.
