Did some searching but did not find what I was looking for.
Are the running board brackets the same for a 1/2 to 3/4 for AD trucks?
No, the front two are the same but the rear ones are different to accommodate the extra length of the RB. The half-ton's are angled foreword. The 3/4 ton's are straight.
In the Facory Assembly Manual there are plan views of frames where you can see the exact dimensions.