Curious if there are any part numbers stamped on the rims? possibly near a valve stem?
I'm speculating they started out as these 6 lug Budd wheels (or narrower version) they are not that difficult to find.
http://rides.webshots.com/photo/2512049150080251109usPlaQ
And they cut the center bolt pattern out and welded in a new plate and drilled the 10 on 7.25" pattern.

We have seen this method before, try this thread:
https://www.stovebolt.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=457491#Post457491


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-