WHO sells the best A-Body strut rod bushings?

Poly is fine at the strut rods. I've used it several times with no ill effects. I got a Poly set from PST.
Yeah, you do need to make sure that they are not thicker than the rubber bushings are. Rubber does compress more so make note of the thickness as it is when compressed, maybe by pressing them in a vice?

The problem is if you’re replacing the bushings the old ones aren’t likely the original thickness to begin with. Heck even if you’ve got new Moog bushings there’s definitely no guarantee they match the originals either.

So then you’ve got to install them and check the position of the LCA, if the bushings are pushing the LCA back from perpendicular to the frame rail (or pulling it forward) then the bushings aren’t the right thickness.

@autoxcuda shows how to cut the poly bushings down here Cutting strut rod bushings for correct geometry?

Thing is if you’re doing all that you have to check for binding and the location of the LCA etc., which means you could just as easily install adjustable strut rods and have a better functioning part anyway.