Not to sound like an [Edited by Moparts - Family Friendly Site - Keep it clean] but if the extra 500 bucks is a make or break on his engine rebuild, he is going to run out of money on a stock stroke rebuild. In that case has has business even pulling pistons out of the block, he should just be running a stock bottom end.

As for fuel mileage, ANY gas engine in a 3/4 ton is going to get crap for mpg, especially with a load behind it. A struggling 318 or a gas v10 in a 6000lb 3/4 ton truck are both going to get bad mpg, now put a 6000lb load behind the truck and see what happens.