exhaust manifold help-tapered or flat flange

[my66cruiser]

Good afternoon. My motor (on my 1966 Town) is a 390 but it is a 1967 two barrel engine (intake is a T code (C7TE....) which I believe means truck plant or something like that). So it is not the original motor. Not sure if the exhaust manifolds came from this motor or the one that was replaced.

How can you tell if you have the manifold with the tapered exit port to the heat riser, or the flat exit port flange (without doing the obvious and removing the nuts to the exhaust pipe and observing)? Did they standardize on the tapered ones after '65? There are two types - tapered flange (for use with the steel doughnut gasket) or the one with a flat flange (for use with a flat gasket with two small holes for the studs and one big center hole). It is difficult to see the manifold's numbers.

Also, any recommendations on where to buy? Most of the Thunderbird joints have them for about $275.00 new. Anyone ever buy one of these new ones and liked the quality?

I am bringing my mechanic all of the parts before he starts the job (yeah I know I could do it myself but this one I will let my mechanic do) and I don't know which one to buy. I am guessing it is the tapered flange that uses the doughnut gasket but maybe you folks here know for sure.

Also, when I have the passenger side manifold changed, I will be using a spacer instead of a new heat riser.

Thanks.

[my66cruiser]

Doing some more research and asking lots of questions I have been told the following:

1) If you have the heater riser valve, then your right side manifold should have a flat flange, so the flat gasket is needed between the heat riser and the exhaust manifold. I believe the same to be true if you are using the spacer in place of the heat riser valve.

2) The other side of the heat riser valve uses a doughnut gasket as its outlet is tapered. I believe the same to be true if you are using the spacer in place of the heat riser valve.

The left side manifold uses the doughnut gasket since it mates with your exhaust system.

The above information is true of a 1966 Thunderbird - if not please let me know. Keep in mind, there are a few different right side manifolds made for 390 motors, some with 2" outlet, some with 2.25" outlet, some with flat flange, some with tapered flange, some with outlet that faces straight back parallel to the ground (for trucks), and some that exit angled downward (cars).

[Massauto]

I have a set of exhaust manifolds for sale if you are interested. PM me if you're looking for used vs. new.