The 283 was a good engine- - - -in 1957. Anything a 283 can do, a 350 will do better- - - - -especially since it has almost 1/2" longer stroke and an order of magnitude more torque. That translates to more low speed grunt, which is what a truck that works for a living needs. The physical dimensions of both engines are identical, and the newest 283 you'll be able to find was made in the mid-1960s, and has probably been rebuilt multiple times. A fairly low mileage 350 that's 30 years or more newer would be a much better choice if you decide to go the V8 route. The only "must have" conversion parts will be a V8 bell housing, motor mounts, and a new exhaust system.
Jerry
