I would make sure the flange on that twisted axle runs true before trying to launch that car again. The reason I keep chiming in and harping on the springs is because I've broken things automatics and stick.
Every time you dump that clutch, you are putting your driveline to the test. You will quickly find the weakest link. a couple of years back, I discovered a problem with my back U-joint. Of course the U-joint broke but so did my driveshaft bend, the casing on my original matching # trans, and the output shaft bent (see picture). The point here is that a $20 U-joint caused many hundreds in damage and many hours of work.
My 4-speed car runs low 12s easily with SS springs, good long Edelbrock shocks, correct pinion angle and drag radials (yea, heavy duty drive shaft and u-joints). It could go 1/2 sec faster with slicks but thats when stuff starts to break and I drive to and from the track want it to be reliable.
I don't want you to spend as much money as possible. Its just the opposite but it seems that you have your heart set on doing things a certain way and thats fine but you might break more things and spend a lot more money than necessary. A Caltrac system is exceptionally nice and will do the job but its probably more than you need. Serious my friend, check out that axle before trying to put power to it. If it has any wobble, things will break.
How about finding some smaller tires and put them on the back to test all of this out so there is less stress on the system? If you were closer, I have an extra set of new xhd springs that I would be happy to lend you so you can experiment. Is there any members close to you who can lend you some SS or XHD springs? More importantly now, can someone lend you an axle?