Can I use 318 exhaust manifold on 340?

340 and 360 heads have a much larger exhaust opening. The pics below show how the 318 gasket (blue) almost falls through the 340/360 gasket. You might get lucky and get it to seal up but then you also might have a leak that you can't fix.

If you go with 340/360 manifolds you'll only need to change the down pipes but if you're working on an early A body you'll have other issues as well.

Treblig