Is there a way to truly identify AAR and TA manifolds over standard 340 manifolds. I see that early castings have numbers on outside and I assume later on inside. Are there date codes I don’t see them on the manifolds I look at. Just curious as I’m replacing headers for manifolds on my AAR.

T/As and AARs didn't use unique exhaust manifolds, they were the same as any other 340s.
I've never figured out why some have raised part numbers and some don't. My T/A has what I am pretty sure (They were in the car in 1978 when I bought it) are the original exhaust manifolds and they don't have the raised casting/part numbers. I am sure some identifying numbers and date codes were cast or stamped in them originally, but I can't see any on mine, and I doubt they could be found after a period of use and surface rusting etc.

At least they all look and work the same...

There is something about the number cast into the surface on the back side of the runners and near the outlet rather than cast outward on the outside/top runners. In Master Shakes case I'd bet the numbers are at that location. Whether that was only AAR/TAs or those are the only ones used on the AAR/TAs, I would doubt it, just not enough made to justify a special run manifold. These are mine but I cant swear to it but they are believed to be the originals, they are in a picture from 84 were most everything was undisturbed. 407 SBD

I only brought this up as I was looking for a set. And I noticed the difference where the casting numbers go so I thought maybe the latter castings have the numbers stamped on backside and early 68-69 cast in front. I also have considered the repop manifolds.