318 1/8 time improvement

Just because it will "hit" an RPM, don't mean it will run the best ET there. You'll have to play with shift points. Maybe next time try 5300 and see how it responds. And play from there... Also, play with timing. It may like 34* or 36*, who knows till you try it.
What do you think about adding the magnum head? With that 1.6 rocker ratio I should get more lift and bigger valves are always good! Lol