You'll need to move the spring perches out some on the axle tubes.
Look for one from a cab and chassis, like a service body, bread truck, or RV, they are usually narrower than the dual wheel version found under pickup trucks.

Just take your tape measure and see what you find and if it'll work.
Some info can be found here, although in that thread it is my intention to use a cab and chassis axle as a single wheel axle there's still plenty of info and measurements to help with using one with dual wheels as they came.
https://www.stovebolt.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=752538&page=1

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-