The engine and trans doesn't necessarily need to come from the 60 - 66 era trucks. Anything from the 70's with the engine/trans combo that you want will be just as easy to install as the same year truck. They are also very affordable to buy the complete truck and use other parts from it too.
Scott

Scott Ward

2 1948 1.5-ton Loadmasters
The red one and The snow pusher
1 1950 3100
1 1955.1 Chevy 6500
1 1954 Chevy 6500 2-Ton
1 1955 1st Series COE 5700
1 1963 K20 (454)
1 1964 C10 (350)
1 1951 1.5-ton Dump Truck
1953 and a 1956 Ford F800

Raising a teenager is like trying to nail Jello to a tree!