http://www.dynatrac.com/ and or some other companies that regularly and professionally build axles from scratch should be able to narrow an axle for you, and re-spline or provide new axle shafts.
Won't be cheap, and at that point you may be better off having a new axle made to suit, from the same folks.
also try http://www.solidaxle.com/

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-