Missed a couple of things here, sorry.

Watto:
Not sure who to recommend for making up a Paradox these days. Down your way, maybe Bill Swann would be worth approaching, and a bloke called Larry Ch_ in South Oz, if you know who I'm talking about. Also, Rolph Bachnick is still around I believe, maybe trading as Safari Arms? (Anybody...?)

John:
The grade is engraved on the trigger-guard tang near the serial number.

Ben:
Regarding the lengths of the other .577 cartridges, longer brass is just an embuggerance as the ballistics are the same but with modern nitro powders, you burn a bit more for the same velocity, and a ridiculous stack of wads or filler is required. Sure, pressure might be a bit lower, but we are only talking 7.5 to 8 tons for the 2 3/4 inch case anyway, so no problem to solve IMHO.

There's always the possibility, however remote, of a full nitro cartridge being fired in a 3-inch or 3 1/4 chamber, far less risk with the 2 3/4.