I was wrong, again. I know, can't hardly believe it myself.
So I checked in on the exhaust shop working on my 77SJ today, and the gasket that goes on the driver's side of the wye pipe, is a doughnut type with a metal insert that centers it into the pipe coming down from the manifold.
The passenger side which has the dampener valve gets no gasket on the bottom with the taper, the tapered side of the valve needs to fit tight and square into that side of the wye pipe. A flat gasket on goes on top of the valve against the pipe flange coming down from the manifold.
At least that's how he's putting together and he has done a lot of 'um.
I have never seen good pictures or a description on this.