Never know what you can find on a forum.
No luck with the web at large.
I'm trying to find a drawing for TR4A front stub axles.
Can pull one and measure but hoping a drawing is available.
Looking for the same for Alfa Romeo Spider too.
May want to put the Alfa front hubs and brake rotors on TR uprights.
Custom spindle seems a reasonable way to do it.
How about emailing Moss Motors technical department ? they are always helpful. Or you can call them to talk to a real person. I've done it before and got lots of good help.
Might try double posting in the Triumph section to get their attention.