Our O.S. car rep suggests a .28-.30-size engine. His thoughts are that an on-road car engine will not be effective. It won't have any low-end torque, which is what you need for your type of truck.

Here are the new O.S. enignes that will be more likely to suit what you want to do:

OSMG2075 13960 .30 VG(P)
OSMG2076 13980 .30 VG(P) SR SAVAGE (accepts roto-start)
OSMG2077 13970 .30 VG(P)-X (has recoil starter)