I would checkout the 360 mileage build and in your current eng I would put a 3 keyway timing set in & adv it 4 deg and dial in the dist subsystems in order: initial/total (initial+slots) at 35 (vac capped) then springs then plug in/adj the can. Not sure if a razor sharp built 318 would be better than a razor sharp built 360 but Scratchn is getting incredibly good mileage numbers with his 318 & he is a truck guy so I would go with his plan. definitely get .035" quench/some mild porting & especially some small tube 1&1/2 or 1&5/8 headers and a free flowing exhaust (mandrel bends/free flowing (somewhat loud) muffs. EDIT the 2.73's and 15" (I'm assuming) tires are hurting you also. As said I would go to a deeper gear