Re: MIL-STD-1553 spec serial data bus. ... [implausibly in] ... the 1950s vintage Hawker Hunter.
It's not even vaguely implausible! Sorry, El Reg, you're out of your depth here!
The Hunter T.8M had a Blue Fox RADAR. The Blue Fox had 1553. Therefore the Hunter T.8M had 1553!
Also... Singapore upgraded their Hunters in the late 1970s. The upgraded Hunters could carry AIM-9 Sidewinders, and given that timescale, the missiles would have been AIM-9L variants, which use 1553 to connect to the host aircraft (e.g. to report status back, initiate self-test, light the blue touch paper...) Therefore Singapore's upgrades in the late 70's would have included MIL-STD-1553.
(And why would you not? 1553 is a very simple, 1mbit/sec fault-resilient bus running over relatively cheap cabling. Easier to use that -- with it's plethora of support and development tools -- than try to invent your own!)