I'd bet the round core will be scarce and spendy - the later heaters [should be in a 55 too I think] have rectangular cores that are much easier to get replacements made for - there are 3 styles of heater for the TF trucks, the factory installed
standard , and the factory
deluxe , as well as the bottom of the line dealer installed, similar to earlier years -
as seen here in my 57 - chrome button with "GM" on face, used on Chevs and GMC's for many years
Bill
