I hope to find another 73-79 ford someday, by far my favorite body style and most heavy duty f150 ever built. M blocks are mixed review. I had one bored 30 over, MSD pro billet distributer, 6a box, Edelbrock intake and carb, dual exhaust out of factory manifolds. 4:10's and c6 with B&M ratchet floor shifter in a 77 f250 4x4 flatbed. My cousin was with me when I smoked an "04 GTO from a green light to 75mph. Only reason he passed me was cuz I let off the gas. I could turn the speedo all the way around back to zero. At least the 7mpg was justified by the power it made. I would spend $2500 on the right truck. Personally, I reccomend getting a pre 77.5 and run an fe block. Swap in a late 70's front end for disc brakes and larger tie rods. My 74 f100 had a pcv valve for an emissions system. Very cool. On the other side of the coin, I have only been able to drool at 2.5 tons. Good luck in whatever decision you make.