Old Leafsprung Land Rovers

I've discovered the reason behind the absence of reverse gear in the 88"...

Knackered layshaft and a couple of teeth gone from the reverse pinion.

Being a series 3 box, you can't just change the gear on the layshaft so a new one is required.  I'm pretty sure it's a suffix A box, but I can't be sure it's the original bell housing, the parts places say the suffix a shaft has a small bearing, does anyone know what the bearing dimensions are so I can confirm what I've got?