How much difference will it make?

Actually the A-500 aggravates the 4.10 gear being a possible problem due to its lower 1st gear ratio. I still think the 4.10 with the tire I have should work.

Cley
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What we have here is a failure to communicate between the frontend and the rearend.
The car is constipated.
For free, you need to lose the swaybars and lower the frontend height. Test run it.
If you have one, install a pinion snubber. Set against the floor with a slight preload. Test it.

Money spending, first rear completion engineering 3 way adjustable E body shocks. Test at differant setting.
Second front adjustable shocks. Test at differant settings.
This is the cheapest way to see what to do next.
I like the slide a link and mono leafs and /6 tortion bars next.
I would be using some 9 inch slicks also and sticking with the 4.10s.

Just my humble opinion which I highly value.