Sounds like you have the original type trans in this truck. They were used in the bigger trucks like the 3/4, 1, and 2 tons etc. That PTO is a bolt on. The transmissions all had the opening for with a cover for it from the factory. Some of the pto's had forward and reverse. It is not a "rare" item but is a little unusual to see one on a pickup. If reverse is over to the left it is the correct vintage for the pickup you have.
