carb/choke question



I know this subject was discussed earlier but I couldn't find it. So, I'll ask again.
I have a 65 falcon ,200, with a remanufactured motorcraft carb.(1100?) The choke housing has a threaded outlet with a rubber plug on it. I'm assuming that there is supposed to be a line connected to it that comes from a heat source. My question is what is the heat source? There is a threaded hole in the exhaust manifold directly under the carb. There is also a threaded hole in the water heated base plate under the carb. could it be a water heated choke?
thanks in advance! ;)
There is an aluminum tube that goes from the choke housing into a passage in the manifold. It draws hot air into the choke.