My first car was a 1940 Dodge, & I think it had that same engine. Very solid engine, but mine was worn some and used quite a bit of oil. IIRC, the same engine was used in Hyster forklifts till the mid 60s, so might be another source of parts. By the early 60s, the Chrysler cars had the slant 6, don't remember when they switched from the flathead, but the early 50 pickups were still available with the flathead.
Fred