For a new 6v motor your options are very limited because 6v automotive motors are almost extinct. 12v motors of various types are plentiful and most of those have 5/16 shafts but you would need a voltage conversion to use it. As a rule, 12v motors of identical size and type as a 6v will pull less amps. Simple 12v 2 wire motors used on 6v will run half as fast since it would almost be like running thru a resistor speed control switch set at low speed. You may be able to find a Packard motor on ebay and since there have been many 12v conversions by forum members, some of those guys may have one laying in their garage. Gerry at Packards Southwest or Tucson Packards may also have one.
If you cannot find a Packard motor, there is a universal motor sold by the Ford and Chevy vendors that will work. Most sell the same motor but prices do vary. It does not have the same look as the stock motor and using it may require a slight elongation of the mounting holes in the housing cover plate and the shaft adapter if you need a 5/16 shaft. Most heater blower wheels of that era used 1/4 shafts with AC blowers being slightly larger and more powerful having the 5/16 shaft.
If you do go with the modern universal motor, it is a permanent magnet motor so polarity controls the rotation direction. You will need to hook it up so the rotation is correct for your wheel which is as simple as trying both combinations and then connecting the correct wires to ground and power. Unlike the stock field coil motors, an accidental battery polarity reversal will cause the permanent magnet types to run backwards.
https://www.classicparts.com/1947-54-Heater-Motor-6-Volt/productinfo/68-005/https://www.dennis-carpenter.com/cars/heater-amp-ac/heater-motor/21a-18527-heater-motor-6-volt-universalThis Post was from: https://packardinfo.com/xoops/html/modules/newbb/viewtopic.php?post_id=267942