I have a new to me '69 F350 flatbed dump with a original Ford v8 360 motor. I had a bad valve and just had the heads pulled to have them re-machined at the machine shop. When pulled the top end of the motor was extremely dirty, they are cleaning it out for me as best they can but I couldn't justify the $2,000 more to have the whole motor torn apart and rebuilt right now which is what they recommended (they recommended it not because they noticed any malfunction with the bottom end just because of the volume of sludge on the top end).

What kind of, if any, flushes or additives should I try to get this thing cleaned out some more? I'm willing to change the oil every 500 - 1000 miles or more if necessary as this truck probably won't see more than 1 day of use per week and a total monthly milage of 200-800.