An under the seat military heater might be an option for you. The problem I see being the hardest to overcome would be the voltage for the blower. That one is 12V. I am making the assumption that you are still running the original 6V system. Another option might be look for an under seat heater for late 40's early 50's GM cars (like the one in my 50 Buick). A quick search on ebay yeilds a few.

1953 Chevrolet 3600
Fried Green T'mater (Vern)
In the Stovebolt Gallery
Caution: Political Statement
Man who runs in front of car gets tired, man who runs behind car gets exhausted.