Hy Joshm, in Canada the V8 engine was an option in trucks from the 55"B" or 2nd series on, 283s were used starting in 57. I understand that in the states the 265 V8 continued to be used up until at least 1958. I have no idea if the V8 was an option on "fleets" as we did not have them in Canada. If you want to swap in a V8 it is fairly simple once you purchase the parts to do so, a front engine mount kit available from many aftermarket suppliers, a truck V8 bellhousing, and a kit for throttle linkage, there was a fan shroud on the original V8 trucks, so that might be required as well, hope that helps.
