Width measurements can be found here.
https://www.stovebolt.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=725027#Post725027

Most helpful and accurate way of noting the width of a front (or rear) axle is wheel mounting surface to wheel mounting surface, it is fixed and not dependent on variables like different rims or brands and sizes of tires.
If you want width outside of tires or rims on the front axle you can measure the offset from wheel mounting surface to outside of tire or rim and subtract it twice from the given WMS to WMS measurement.

You may be better off to swap the axles or brakes under an original frame? See the link above as well as.
http://www.stovebolt.com/techtips/bigbolts/p30swap/
and http://www.stovebolt.com/techtips/wheels/

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-