273 Exh Port MisMatch

Can I Weld-Up this Lower Corner where the Manifold hangs over the surface?
Will a Mig or Flux-Core even Stick to the Cast Iron?
You're about to go down a rabbit hole that doesn't even need to be considered.
You had the end gasket reversed, that is all.
Avoid all this, and just ditch the header gasket entirely. Manifolds were never intended to use gaskets anyway, and as you found out can cause more issues than they solve.