There are some interesting differences between your housing and mine. If I were to assume, I would say that you have the school bus set-up. It appears that that fitting that comes out toward the drivers side was probably for an additional heater since it is below the thermostat on the bottom half of the housing. I think my second fitting (on the top side of the housing)that comes out on the passenger side was the by-pass feature for the 2 or 2-1/2 ton trucks (non-school bus). If you'll notice, mine does have a third boss (also on the top part of the housing) that could be tapped and used. Maybe it's just a slightly different design from a different year. Maybe there is someone here that knows for sure. I don't know why you couldn't just use that fitting on your housing and eliminate that spacer you got from Langdons. Anyone???
