On my 53 1/2 ton I just pulled the heater core that came with it and it is a square one about 7x8 inches. I am going to take it to NAPA and get a 12 V fan that will fit the mount strap on the back tomorrow. I have defrost vents in my dash but no ducting or places to hook the ducting to on the heater core, any ideas?

If you need a tool and don't buy it, you will find you have paid for it and don't have it.