6" lift = what axle shims?

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The truck I'm working on has a 6" suspension left, but the rear pinion angle isn't the greatest...
Instead of going higher in the rear with a shackle flip, I was told that I could use shims to correct the angle.

Anyone have any experience doing this?

If so, can anyone tell me what degree of shim I should run to help correct things with this lift?

I've read for other make of trucks with 4" lifts, they were saying 6º shims would work, but I wasn' able to find any recommendations on a 6" lift for an older chevy (1980 K10).
I'm guessing something like 8º or 10º, but I thought I'd ask here first.