Hi Rene, of course i bought it like this, you seems an expert and you could be right but according to me before the '80s/'90s collectors of wrist watches didn't exist, before that period people didn't care about references and factories made watches using the pieces they have in their stock…in this case it could be that Breitling have made more cases for the ref. 1765 and then looking that in some part of the world people like more the ref. 7650 they used some of these cases to made the watches they could sell more quickly!
The fact that you have seen other of them could confirm it ( have you seen also the opposite thing, a 1765 with a 7650 back? )...considering how rare is this model for me it's hard to think that someone find some 1765 cases, some movement cal. 178, some original dial for 7650, some original bezel for 7650 and assembled watches!
According to me only the Breitling could do this thing, they didn't use to throw away watches' pieces and if they have a lot of 1765 cases but that model was hard to sell, they used those cases to make another model!
Honestly i don't know, this is what i think but, as you told me, just my thoughts…if you are interested in doing an investigation and you think it would be useful i can send you the full serial number in a private message!
Have a nice day,
Francesco

: HI Francesco , thank you for taking the time to reply

: I understand you bought it like this ?
: problem is that although I have seen 1 or 2 others (this being the
: 3rd) I have a hard time reconciling where it would fit in and
: hiding the serial number doesnt help either in investigating

: IMO , collectability will always be problematic unless someone can
: come up with more of these and the ref 1765 attached to it but
: one of the difficult parts is getting provenance. An AVI/CP
: version with the 1765 reference seems questionable as at the
: same time Breitling already had the 7650 ? And when these were
: made , '68/69 , Breitling and other Chronograph makers were at
: the height of their success with little reason to cobble up
: watches like they did a decade later ? To me it looks like
: someone had some parts that almost fitted together and made a
: working watch out of it ?

: and a last comment ,

: look at the overall condition of the Bezel (NOS/New) and compare
: that with the case (scratched and rebrushed) .. doesnt seem to
: 'come together' if you know what I mean ? there's a mismatch
: between the worn case and the brand new looking bezel

: anyway , as always , just my thoughts

: Rgds
: Rene

: p.s. if it had the correct caseback I would have made you an offer
: !