6000 6200 should be a good shift point
1 adjust kickdown
2 do a cranking comp test
3 ditch that carb for a holley dp 650 700 750 the 700 is nice has the rear 50cc acel pump
OP said stock converter and 3.55' s, and a cam that could possibly hurt his bottom end
I would choose a vacuum secondary like an AVS, Thermoquad, or Holley 750 vac sec
