L6 250 Exhaust Manifold to Downpipe Question

[John in OH]

I’m currently replacing the intake/exhaust manifold gasket on a 1972 GMC C10 with the 250 L6 engine.

The exhaust manifold to downpipe connection is giving me fits. When I bought the manifold gasket kit it came with a doughnut gasket, but from other postings here, I don’t think my connection requires the doughnut. And after several hours of trying, there is NO WAY this connection can be made to work with a doughnut! My pipe looks kinda like this:



The cast face of the exhaust manifold has two studs and an internal chamfer so it “appears” that the downpipe may fit directly into the manifold without the doughnut. There is a clamp flange that slides on the downpipe and pulls the downpipe up against the manifold face via the two studs.

But I can’t believe that this metal-to-metal contact won’t leak! Am I correct? Will it probably leak? The old studs are questionable so I hesitate to torque them too much. Has anyone used a gasket of any kind, or high-temp sealant to assure a leak-free connection?