Early a exahust suggestions?
not sure what the air injection boss is. I know my heads have holes that are plugged up that were air injection purposes but they have small allen plugs in them is that what you are talking about? This sucks but gonna have to fix it
To bad you had to leave the 273 manifolds on,your really choking your 360.
Having said that,first thing you need to do is take the manifolds off,and make sure all your air injection (holes) in the 360 heads are blocked/sealed.
Allen plugs with a high heat sealant. These need to be sealed first. The exh man gasket "does not" seal these.
Second,look at all mating surfaces,and make sure they are flat,with nothing protruding out.Use a wire wheel,file,to smoothen any rough spots,if you cant take them out of the car.Put rags in the cylinder head holes,so no debris goes in.When finished, clean with accetone.
Third,look for a set of high quality/thick 273 exhaust manifold gaskets.
No sealant should be necessary.
Put them on,torque to factory specs,drive,let cool,re-torque,and you should be good to go.
