I just (this spring) installed a fresh air heater system in my 49 and it came with a 6V motor that I replaced with a NAPA 12V - was over the counter even up in my remote neck of the literal woods:

NAPA M6478

Was an absolute direct replacement. Works great.

1949 Chevrolet 3/4 Ton - Still Solid. Regular Driver
OT Vehicles:
1925 Hudson Brougham Super Six
1950 Chevrolet Styline (Parts)
1952 Canuck Pontiac Sedan Delivery (Well Underway)
1973 F250 4x4 Highboy
1977 F250 4x4 Lowboy