[sstock]

I decided to tackle my heater, it had been inoperable for a decade or two according to the previous owner. Upon disassembly, I found the fan motor to be toasted and the heater core to be original and evidence of leaks. This is the thrift heater in the 1964 GMC, even though it is a full airflow heater it has a smaller core and single push pull damper and fan switch. The core measured 7-1/8", based on a poster in this thread I decided to up grade to the larger core which is a full 9.5". Oddly enough the core mounting plate is stenciled for the larger core, so it was a matter of jigsawing the metal plate. I found a full size core from the filling station, beware there are vendors that sell cores that are only 1.5" thick instead of the full 2.5", not nearly as efficient and you will have to fab up a mount for the thinner core. The core from the filling station fit like original, literally took me less than 5 minutes to fab up the mounting plate to accept the bigger core. Here are some pictures of the heater sheet metal after I glass beaded it. Some others finished. BTW, it blows hard and hot, a great modification and cost nothing more than a regular fix.
Steve