phunk, I agree with you, the difference in grip has come from the changed link arm lengths and the way load is supplied to the diff , the neg. pinion angle is unwanted but thats what works best on drag cars, speedway cars and rally cars.

It is another option to cut off link arm mounts and rotate the diff to a desired degree and weld them back on, in my eyes its a painful way of experimenting though, after the initial time it takes to make the adjustable arms it takes less than five minutes to adjust the angle.

ok a little info I can add, as it seemed to launch pretty well out off the hole. Was a rx4 I had together once that on luke warm 245x17inx40ish slicks would get moving quite well. You could let the clutch out at 5500rpm and would just get out of there.
No idea what leafs are under it but they were different maybe lovells ? but as the set-up was quite stiff.(extra leafs) It had an added panhard rod bar and another bar that mounted from the top of the diff housing to inside the cabin and located to bracketry were the back seat should have been.
what looks to be the case before this modification. is that it was added as the diff flange/tailshaft yoke were wearing through the floor.this mod seemed cheap and effective but seemed to work well not sure you could talk you way out of it in a street car but

No, actually it is to do with the pinion angle.
You could go to the lengths of repositioning the arm mounts on the diff to bring the pinion angle back but you will find that the traction will be lost again.

Don't ask me exactly why it is so but thats what happens.

On a side note, sedans in speedway typically use 2 - 3 degrees nose down on pinion.

Another thing to bear in mind with changing the pinion angle is that when you increase positive acceleration traction you are decreasing negative acceleration traction by the same amount. i.e. the more traction you gain on acceleration the less engine braking traction you will have.

Monkeywrench, what you described is usually referred to as a torque arm and reduces the amount of spring wrap on high hp leaf sprung cars.

Lemonhead I see where you are looking now. And I guess once the sump mods etc are done, its only a matter of adjusting the height of the engine and box mounts to vary the angles back and forth.
If the angles were getting bigger I guess you would look to the other way.

MLS I cant see how pinion angle can attribute to traction vs no traction in a cornering example. I can however see it attributing to power.
I beleive the noticed difference in traction is from suspension geometry not driveline angles.