Thank you for presenting this very interesting question and the photos. A few reactions, as follows:

-- I have never seen an Autavia dial in a Carrera case, that was made this way by Heuer (special order or otherwise). Yes, over the years, we have seen many Franken watches, of all varieties, but I am confident that we have never see Heuer use an Autavia dial in a Carrera case (or for that matter, a Carrera dial in an Autavia case). They just were not in the habit of mixing and matching parts from these models.

-- This dial is a rare one; Reference 2446 dial (being three registers) with the Tachy scale printed on the dial. We have seen numerous samples of these dials floating around for the Reference 3636 Autavia (two register), but not for the three-register model. So this makes me think that was probably made back in the day, and not more recently.

-- These Tachy-on-dial Autavias use different hands than the standard Autavias, and your hands seem to be the correct ones for this dial. So this tells me that someone had the correct Autavia, and put it in a Carrera case, rather than having a Carrera and switching for the Autavia dial.

To my eye, this is a great looking watch, regardless of how or when it was produced. My suggestion is to enjoy it, the way it is!!

Another approach would be to try to find a correct Autavia case, and do the transplant, but that depends on your preferences and your appetite for this sort of project.

Jeff