I have the recirculating type and it works great. Classic Parts sells a reproduction heater box, heater core and motor. The price has gone up significantly since last year, however.

https://www.classicparts.com/1947-54-Heater-Box-Round-Style/productinfo/68%2D206/#

https://www.classicparts.com/1947-57-Heater-Core-Round-Recirculating/productinfo/68%2D222/

https://www.classicparts.com/searchprods.asp

1950 Chevrolet 3100 (Ol' Roy)

1939 Packard Standard Eight Coupe (The Phantom) | 1956 Cadillac Coupe de Ville (The Bismarck) | 1964 Ford Galaxie 500 coupe |1966 Ford Mustang (Little Red) | 1969 Pontiac GTO (The Dishpit) I 1979 Ford F-100 | 1976 Ford F-150 (Big Red) | 1995 Ford F-150 (Newt)