there was a factory installed standard heater with a round core in at least 57, [maybe 55-57], and a different standard one 58-9 ... there was a factory installed deluxe heater that I believe was the same 55-59, and there was a simple dealer installed heater for 55-59 that may also have been the standard in 55-6 [and I've seen it in AD's] .... find some
pics here, mostly of the deluxe, except for the ones at the beginning
Bill
