A3 has a pretty PAFish voicing, to my ear it's especially great for neck hums. Quite low output, though, even compared to A2.
The low end is reduced enough that it doesn't get mushy like A2 can, and the mids & highs shine a little brighter.
I'd say it's well worth trying, although you might want to raise the pickup a bit from where it was.
An A3 swap takes output of the Custom wind right down to the upper range of vintage output.
I remember the Custom3 as having been a viable alternative to 9½-10K hot-PAF bridge winds.
A4 is really, really nice for neck humbuckers in most cases. I like to say it has sort of a split personality.
Played clean it tends to have good definition and a nice sparkle, quite pick-responsive and dynamic.
Given some gain & volume it takes on a whole different character, smoother and singing yet a little raw. No longer polite.
Overall, I've found A4 to be nice and vintagey in both tone and feel, good for neck or bridge.