If my memory serves me well:
- the forward header is almost straight downward as in early 235 (and 216) exhaust manifold, and the end has a beveled opening (fitting surface) - donut gasket
- the rearward header is more angled rearward as in 1954-1963 single 235/261 exhaust manifold, and has a flat opening (fitting surface) - flat gasket
If you have two different fittings on the two exhaust pipes, using the earlier donut seal/gasket in the front, and using the later 235/261 flat-gasket in the rear will work.
I have successfully used donut seals at both points, even with a flat rearward exhaust pipe.
What types of fittings are on the ends of your two exhaust manifolds, and on the mating sides of your two exhaust pipes?
