I used the vintage air COMPACT heater/demister
It has two hose connectors for the defrost vents as well as a trapdoor that opens to let hot air into the interior. Comes with all controls etc.
http://www.vintageair.com/catalog.asp
Go to heaters from the index and you'll find 2 heater/demisters.
I used the one on the bottom of the page because it is more compact