Ok Simon, nice quartet of Autavia's. I'll give you my opinion on what to do.

Firstly the 11630 GMT - You have to keep in mind i prefer these on leather rally straps.
The 11630 case is taller and in a sense feels more top heavy than the earlier 1163 model. The grains of rice GF bracelets with HLF end pieces are interchangeable between the 1163 & 11630 (although fit better to the 1163 case) but IMO matching your GMT with a rice bracelet will make the top heavy 11630's feel even taller. It may well have something to do with the delicate feeling of a rice bracelet VERSES the chunky feeling of the 11630 case. The later plated style bracelets are heavier to hold and sit a little chunkier on the wrist, i feel they better suit the 11630 case.
Here's a nicely paired couple from Peter Moller's website http://www.heuerwatches.net/Autavia_11630_GMT.html

The 2446C - lovely clean example
I can understand your asthetic draw towards the MH bezel due to its balance but for the sake of originality i would leave the tachy in place. I think the best way to sum up the difference in the tachy and MH bezels would be to say that the MH is mostly there as there are no numerals on the dial. It is to make it easier for those that struggle to tell the time without the visual aid of the numerals. There is an unofficial way to use these bezels as a GMT second time tone by rotating the bezel to the hands to indicate a second time zone (however in this case that voids the use of the Minute scale on the bezel).
The tachy scale means racing heritage in my mind. They really were used back then to time acheivements on the race track. From speed MPH / KPH & lap times.

We all cringe when we see eBay Heuer disasters offered up with incorrect or replacement parts. In this case it would only be you that knew the watch was no longer original but it is my bet that it would gnaw at you in the back of your mind that the watch is no longer as it came from the factory.

Good luck with your decision - Darren

: I am looking for some advice on my 2446c and 11630 GMT, please will
: you let me know what you think:

: 1. 2446c. I am sending it off for a service, what do you think
: about the T insert? I prefer the MH one but I already have a
: 2446c and a 7763 with MH inserts. If it was your watch would you
: try to find an MH insert or would you keep it as it is?

:
:

: I like the 7763 as it is with the MH insert and leather strap so
: won't swap the two inserts over. I also think that the three
: watches are suitably different that I will continue to wear them
: in rotation

:
:

: One of the reasons I have thought about the swap is from seeing
: this still from The Exorcist. The watch looks more balanced with
: the symmetrical insert:

:
:

: 2. 11630 GMT. I like it on the bracelet but should I try to find a
: bracelet for it? I have a GF bracelet currently on an 1163, is
: it easy (and relatively affordable) to find end pieces to fit
: the 11630? Or should this watch be on the Oyster-style bracelet?

:
:

: Going back to the T and MH inserts, what was the difference, does
: one measure speed and the other one distance?

: All help gratefully received.

: Thanks,
: Simon