Dimension of 75B vs. pre-b

[Sturubu]

Aside from the trigger guard, are there dimensional differences between the models?  There's a leather worker who I've heard does excellent work, but he only lists the form for the 75B.
I've searched high and low, and can't find anything showing the physical changes between models.  I have also seen posts with makers who build for pre-b's - just nothing defining why to go specifically with one made for a pre-b.
It would be cool to know that he could modify the trigger guard part and make a fit!