Torque converter
I would lean more towards converter, Last year I rebuilt my 360 pump gas motor (9:1, .484 purple shaft cam, J heads) and stepped it up considerably. Fresh motor is 11.7:1 ported J heads, with a 2.05 intake valve and more cam (292/299 .508 comp hyd.) used the same converter that I ran with the old combo 10" turbo action that flashed 4200. went from 1.58 60 ft and 11.90s at 110. to 1.62 60 ft and 11.50s at 113 with the new combo flashing at 4500. After trying everything else I finally put an 8" in that is still too tight but it now goes 1.52 60 ft. and 11.20s at 117. Car weighs 3150 with me in it. 4.56 gear and 31 tall tire, I launch at 3000 shift at 6000 and go through the traps at 6200