I know the style of the brackets changed but do they interchange from a Poly to a LA engine ?

pretty sure it will be the same 70 and back, vs the 70 and up style.
a/c vs non-ac etc... have to match up.
so round backs only.

since pretty much everything else bolts up, I can't imagine the alt brackets being different.

Obviously, the heads are different. So if the bracket bolts to the head, then no is probably the answer.

Very good. Im going to swap a Denso alt onto my fathers Poly 318 and was just making sure. Thanks guys.

The 65 poly 318 and LA 273 used the same alternator bracket, but had two sets of mounting holes, one for the 318 poly head, and the other for the 273 wedge head. The 1965 A/LA bracket will also bolt to a later 318/340/360 LA. But since the later LA brackets don't have both an A and LA bolt pattern, I wouldn't think they would work on the poly without modification.

Now whether a Denso alternator would work with a poly alternator bracket, if that's what you're asking, can't say.

I used the later model square back on my poly.
BUT to get it to work, I needed a longer swing arm.
the 10 dollar chrome GM style one with some spacers to kick it out far enough away from the block worked for me.

you can kind of make it out here.