'40 hot air heater

[Uncle Bob]

Okay '40 gurus, a little education please. So I figure the pictured unit is a hot air heater coming off the pass. side exhaust manifold, yes/no? Were these a factory or dealer option, or strictly aftermarket? I figure it must have some factory support since the blind port is stamped in the stock firewall. Are they any kind of effective or offer more promise than performance? Anything you can add will be appreciated.

I tried a search in the early v8 section alone and got a lot of hot water heater references (searching for "hot air heater", not a very selective search even in advanced) and found one fairly beat up unit in the swap section that's been for sale for over 2 years. Guessing not much demand for these?