i'm set up real close to what you have.
71 dart, 408, powerglide, 4.86 gear, 5,000 stall, 29.5x9 M/T slicks. I have adjustable QA1 shocks on all 4 corners of the car, slant 6 torsion bars, and super stock springs that have every leaf in front of the axle clamped. the rear clamps are still on behind the axle just as they came. I leave at 3,000 rpm on a trans brake. car picks the front tires up about 6-8 inches and sixty foots 1.45-1.49 with a powerglide.
as mentioned already you may have a little too much gear. you are running the same gear as me basically, but you have a 2.40 something 1st gear ratio in your tranny vs a 1.76 in mine.
I would start out like this.
clamp the front of your current leaf springs, and unclamp the rear since you are foot braking and not letting go of a trans brake or dumping a clutch.
go with a taller slick to kill some gear, and give you a bigger contact patch
get the front end working!!!!! this may be the most important.
get at least 5-8 degrees of pinion angle. this is very important. if you need more then go to an Advance Auto Parts store and look where they have their helper springs, spring clamps, and such. they will have packs of pinion angle shims in that section that come in 2 degrees and are MUCH cheaper than ordering from somewhere.
try to get at least 5 inches of travel in the front end before the tire leaves the ground. leaving the factory strut rods and going to one with solid bushings and heim joints will help maybe as much as anything. trim the upper control arm bump stop down to gain more travel, or take it off all together as long as the side of the shock doesn't hit anything after you do.
I could only get 4 inches of travel out of mine, but more is desirable.
one more trick that will make the car hook and run fast is to add 100-200 pounds of weight in the trunk as far back as possible. just use something like a ballast box and make sure it is secure. I have seen many guys do this and pick up on ET even though they weigh more. if a light car won't hook, then being lighter isn't doing you any good.
try that first and I think you will be surprised. the areas of concern after doing those things would be if the rear end and body are seperating too quickly at launch and shocking the tire. in that case the 50-50 shocks would have to make way for an adjustable so that you could slow down the seperation and let the tire plant properly without being hit too hard.
the pinion snubber could also be used at this time before going to super stock springs. 1/2 inch from the floor is usually a good place. I have one on my car but it doesn't even touch the floor with the springs clamped up. I have it set at 1 1/2 inches just in case a clamp or something breaks. at least it will save my u joints from failure.
good luck and let us know how it turns out.