A 6V-53 should fit in there. I believe there has been a few put into pick-ups and believe there is at least one on You-tube. Altho if it were my truck, I would be happy with a 4-53 in a truck that size.
I'm going to guess that the GVW is about 19,500.
I had a '62 GMC 4000 with a 305 V-6 gas and it pulled just fine. The GVW on that truck was 19,500 and many times I would go over (back in the old days).
Bill
