I don't think those heaters with 2 motors were made into the 12V years, pretty safe bet it has 6V motors unless the truck has had a spendy conversion to 12V .... most of the small motors have voltage imprinted on them, otherwise if you can round up a 6V battery or a charger with dual voltage function you should be able to tell, a 12V motor would have a hard time starting on 6V and turn way slow
yes, you could use a pair of reducers, if there's room to mount them so they safely dissipate the heat
Bill
