Yo Trev, well not completely wrong, I figured that the A10's up to ~'50 which I gather is when the A7 Longstrokes finished, did some research last night, and have found the part numbers on DragAnfly for what it's worth- they don't have the layshaft constant-mesh I need to replace.
Some parts are listed as '47-'49, some '48-'49, some '48-'50, and some '47-'50
I already determined the main difference being in the dog arrangement (as per photo with pre-requisite circles and arrows) and sprocket seal, outer cover/w kick return spring, the camplate detent plunger has a chisel end instead of a point, and maybe a couple of other things.
I have a couple of the later boxes, one which came on the 23.12.52 engine (into which I grafted C/R gears) so I think I'll reno a STD one of those to keep it simple.
The only issue with this earl box, is whine and slipping out of third gear, but I'll go to that thread.