Black plate or orange plate on the transmission?

F54L is a 235 mated with a Hydra-Matic transmission on a 3700 truck.
http://chevy.oldcarmanualproject.com/chevyresto/54057.htm

A 3700 was a Forward Control Chassis - a step van - it would have had a Carter updraft carburetor as you describe, I think.
http://chevy.oldcarmanualproject.com/chevyresto/54151.htm