Other than center punching and drilling and easy out, is there any other slick way of removing old broken cast iron manifold studs ?

If it's not recessed you can weld a nut on it.

These are old and tight and corroded.

Have been soaked but still twisted off.

I guess could try weld nut on what is left, and who knows maybe it will turn out or just twist the stud again.

thanks

I've removed a bunch

They usually come out fairly easy if you heat the cast iron around the stud red hot and use pipe wrench pliers (after the stud is no longer red) to screw them out.
That is if there's enough left to get hold of.

Be sure and let the cast iron cool back down slowly