Poly's had adjustable valves. Just for kicks, I think I would run through the adjustments to be sure they are right. A poly with 3:55 gears should run bit stronger then 70, but the single exhaust is pretty restrictive, and the 2bbl carb is pretty small. Poly's can be made to run pretty strong, they were good motors. Bean counters (the heads were expensive to make) and narrow engine compartments spelled the end for them. 1966 was the end of the poly in production vehicles. Some did show up in commercial vehicles into the 70s, but they were probably left overs. Gene