Hi drove me 78 first time today, went to a quiet road to check / try out, not to harsh as running in.
Pressed pedal to about half and got instant 3000/3500 rpm, with spinning passenger wheel only, would then change into 2nd & keep spinning till about 40 mph.
later locked auto into 1st stabbed it at 25mph no spin just good acceleration. Also other problem the rear seems to steer itself when going over bumps quite noticeable. the suspension does seem very soft all round can bounce the car easily.
What can be done to improve things, as shame to have the performance go to waste.
2.41 open diff, standard torque converter (1500 rpm), th350 with shift plate, 355 9.6:1 cr, mildly portted 624's, comp xe 262, 600vac/sec, headers + freeflow dual sys. tyres are 245/60/15 standard radials inflatted to 25 psi.
The only modification i have heard/read about is to re-drill the front leaf spring mouting hole 3/4" higher up, any other idea's, thanx.

First thing id do is change to a posi unit and get the coresponding gears. 2.41 is VERY high {low numerically} id think a 3.23 or even 3.55 would work much better

sounds like wheel hop to me! I definately agree that a shorter set of gears (numerically higher) will help you out a lot. I also would recommend some sort of traction device (traction bars) and subframe connectors if you don't already have them. The traction bars bolt onto the leaf springs and keep them from twisting and releasing, thus reducing wheel hop.