I ran the original 6v blower motor on 12v for awhile, it really screamed. The original switch gave in and I got a new blower switch from one of the vendors, the plastic knob melted after awhile and the wire resistor broke. I decided to get a 12v motor. This was over 20 years ago so the internet was not an option. I took the 6v motor to the local auto parts store and matched it up to a modern replacement. The 12v motor was a little smaller, but it worked for many years, still works. The heater core eventually developed a leak, so I took it to the local radiator repair shop. They hooked it up to air and put it in a vat, but found no leak. The shop foreman said to increase pressure since it’s not uncommon for these to get used with a newer engine with higher pressure. They did and found the leak and fixed it. I had put a newer engine in it, a ’54 235 in the ’47 truck.
I looked for the receipt but didn’t find it, so I took some pictures of what I have. With the number on the label “PM3608X” I was able to find it is a Siemens blower motor I originally purchased at Napa. I don’t see it on their website, but you might find they have something that works. They have a few motors without squirrel cage, and many with. You might find one with a squirrel cage and swap that out for the original. Make sure the motor isn’t too big, and the shaft size is correct. Here’s a link to the motor I used (only one left) for $45, I think I paid $35 20 years ago.
https://www.bmebearings.com/products...motor-12-volts
Another option, you might find a motor shop to rewind the original to 12v.
Well, I just looked and you can get a replacement from one of the on-line vendors…
https://www.classicchevy.com/1949-19...-252023-1.html
And, I just re-read this thread including everything that was added since last week when I first read it. I guess I’m late to the party.