There is a lot to consider when going at a project like this. Mileage on the existing motor, tranny, rearend, etc. A Magnacharger or Whipple would be the easiest and cheaper route than the 502 swap. But if the motor is tired and worn out, then a motor swap may be in the cards... A 502 swap hasn't been done by any members on this site as far as I know. Here is a decent look at a 502 built for towing: Click here. From there, I would recommend (since it is paid for) selling it and buying a diesel since he will be towing...