Especially if you are footbraking, see if you can borrow a proven 750 some time when planning a test & tune. Maybe a 2" 4-hole spacer too. If the set-up (jets/squirters/pump cams) is off, it can affect how the converter flashes as well. Check for proper closed & open valve spring pressures.
I had a very similar combo in a home built (bought from a friend) 2x3 frame 2800-2850 lb Challenger in the '80's & 90's. All time bests were 10.22 @ 130-131 and 1.37 60'. But it was a std. stroke 360+.040(?) (cut down DC 355 pistons) with 750 DP, .585" flat tappet cam, Harland Sharp 1.5 rockers & a little less compression. Heads were ported with the Direct Connection porting templates, same tire, gear, trans & converter. Converter was a Turbo Action 4200 and had JW simply freshen it over the years. I don't recall the actual flash. I tried shifting at 7100, but found it ran the same @ 6800! Suspension was ladder bar/coil overs all around, but nothing fancy. Geometry never seemed right, but it ran faster the lower I made the car and more consistent when I added 50-70 lbs to it later in its life.
I always tried to stay conservative. I guess I had the combo figured out, but its long gone. Hope all the suggestion help you with yours.
