1974 power wagon questions

When my 68 3/4 ton with 3.55s and 9.50-16.5 tires; had the 318 in it I got up to 16 mile gallon after tweaking the crap out of it over time. Pulling a trailer it would get 8 to 10. My trailer I'm talking about is a four horse trailer with horses in it.
When I switched it over to the 360 I'd only get about 14 but I'd get 12 pulling the same trailer that the 318 got 10. So that was a 20% increase in mileage. I was hauling horses All Over America and in parts of Canada. The one big mistake I made on the 318 was I used slick 50 oil treatment. It coated the cylinders and got me a couple more miles to the gallon but it made it start using oil. I also tried splitfire spark plugs they were only good for one mile to a gallon.

If you got the money do the stroker.