Pre-post war B series gears

[Rupert]

Hi, can anyone confirm whether or not individual gear pinions are interchangeable between the 37-40 B series gearbox and the post war 46-48 B31/33 gearbox?
The gears all have different part numbers pre and post war but visually seem identical (other than the layshaft 2nd and top gears being one piece post war), the only difference being the post war gears have a groove machined around the middle of the teeth - to identify them as post war?
I'm trying to build up a box from parts, just need to know what I can and can't use...
Many thanks, Rupert.