I am Talking about the 74-76mm forks and later 77-84 35mm forks here........... The 72/73 34mm forks would also fit in but i have not done actual measurements with those 2 earlier forks.
I bought an 80 Special that had a cut down 34mm 74-76 front guard on it.
There was some talk by Hugh, (HHB), how the 34mm forks wouldn't work with his Fork brace, only 35mm forks would work.
I did some research using sets of forks i have because of the HHB problem and here is my conclusion and findings.
34mm Forks guard mounts were part of the mold when the lowers were cast.
As can be seen in the pic the 34mm guard mounts holes are 60mm Center to center The over all width, outside to outside is 81mm. That's 10 1/2mm from center of hole to outside of the mount.
35mm fork guard mounts look to be welded on after the lowers sere cast.
Again in the pic, the 35mm guard mount holes are 60mm Center to center. The over all width, outside to outside is 75/6 mm. That is 7 1/2 mm from center of hole to out side of the mount
74-76 34mm guard will swap with the 77-84 35mm guard and vise versa