Dave Dume,
K & N air filter, Diamond Fire plugs, dual exhaust, static timing at 5' ATDC, rebuilt 2 bbl, 14" tires about 11 to 12 miles still. Fun to drive, a little gas Hog.
You need to get out of this nonsense of timing the car ATC
Any decent running 318 with a stock cam should be able to get 17--?? on the highway. Back in the early 70's I swapped a 340 into my 70 RR body. Big heavy Dana rear, that car weighed over 3800. It got 17 1/2 on the highway.