There are two different 12v motors readily available today, I can search and repost but I recently covered heater motors in a different thread.
Should be one that fits without drilling out the fan.

I'm presently running a 12V replacement motor from NAPA in my GMC with 6V. It runs fine, as if on medium or slow all the time. Later I'll upgrade the truck to 12V, that's why I put the "wrong" motor in.

•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-