...of what the original bezel may have been.

An H bezel would have some redundancy given the dial already has 6 and 12 arabic markers. A 1000 to 60 Tachy would have overlap too, plus the watch seems to predate T bezels on Autavias. An M bezel would have no redundancy and neither does Mick's 13-24 one. I'm never entirely convinced of the utility of a rotating minute bezel though. That's if they were even thinking in terms of redundant information - quite possible given Heuer were always a serious timing company.

And I wouldn't discount that 13-24 bezel by any means either. The 3 might not be a match for 3s on the known bezels, but you only need to look as far as the 63 marking on the Tachy scale to see a similar, if more stylised example.

Heuer had been using flat top 3s on their Tachy scales for some time. Late Autographs have them in the same style as this Autavia, but even early ones have a 3 with a flat top:

Note that the 3 for 35 in the seconds scale is rounded though, so we know they weren't concerned about mixing fonts on a single watch.

As it stands, we have seen two watches with the dial mounted; Mick's has a 13-24 bezel, the other a gold-coloured one apparently from Rolex. So provisionally, I guess we take it that Mick's is the original and we look for more examples and/or documentation to prove or disprove that. Could be a fun journey or we might struggle to find more, either way it will be interesting finding out.