Hi Nick,
still no luck in my quest.
Mmmm ... are you sure what you're after actually exists? As posted:-
was given a partially completed race bike project a year ago. By the numbers, DHxxxxx, it was made in april 73.
By April 1973, the BSA Group was in receivership, being broken up to separate Triumph and the BSA marque to combine with Norton and Villiers to make NVT. Afaict, NVT started the '1974' model year in June 1973. A bike built in April 1973 was the Receiver using a few Small Heath employees to assemble whatever could be assembled from bits in parts bins?
Fwiw, I do know that, early in its existence, NVT assembled some 'concept bikes' based on ex-BSA models, one of which was a B50 badged as a "Norton International" (is that a small earthquake or many Norton luminaries revolving in their graves?

) ... However, given the penny numbers total sold since '71, I suspect said "Norton International" would've made a lead balloon look like a flier?
Also bear in mind Alan Clews got to haul away a lot of (all the remaining?) B50 bits and turn the engine and CCM into a roaring success? I'm suspecting a
real honest-to-God '74 is going to make rocking-horse poo look positively common?
Insofar as a TR5T is a Triumph 500 twin in a look-like-a-B50 frame while a TR5MX is a complete B50 500 cc single with just Triumph badges on the tank?

Also specifically TR5MX (and B50MX) electrics are zombie (risen from the dead to consume owners' bank balances) Energy Transfer. The alternator is a RM22 - essentially about one-third of a RM21 stator (a section containing a pair of stator coils plus adjacent mounting holes) charging an AC ignition coil.
TR5T
1974 model only having 900 + units made,
Aside, the US importer had ordered, and NVT had planned production of many more, scuppered by the Meriden sit-in.

Hth.
Regards,