Specific question about "bolt on" fork swaps.

[robo]

I think that I've read every thread on here about front end swaps. There is a list available of which bikes have the same upper and lower bearing diameters (outside and inside) as the XS650 (25 and 30mm.) It seems to me that those would be the easiest swaps without needing to change stems or machine or shim anything, if I am getting this right. My question is, does the width of the bearings (15 and 15.2 on the XS) matter, or just the diameters? All the stems with the same width bearings as the XS seem to have similar (smallish) sized fork tubes, and I was really hoping for a 41mm diameter, right side up, fork.

Thanks.