Dear Stewart, incidentally I have just posted to Museum's lovely 510.502 stating that none of the 510.5xx were ever assigned (bar the AMI of course, I should've written 510.50x!) ...funny how it may turn out so differently.
However as far as my knowledge goes these watches have a very strong military feel but were never assigned officially - the same as the Sinn 156.
Maybe some pilots had their own watches and got them engraved on a personal basis?
A few years ago some photos popped up with a L5100-based Heuers that looked even more military, sandblasted finish, white hands the lot.
Still most doubted their originality - not as Heuers but as assigned watches.
Indeed yours does not seem to match the usual pattern of IDF markings, but here I am venturing into unknown territories for me, I am sure others can help.
Cheers,
Fabrizio