340 exhaust removal

The hole in the manifold is about 3/8. With it bolted in place it serves as a pilot for a 3/8 drill bit, then a 3/8 shank center drill ( #4 if my memory serves ).
Grind away any stud remaining to flush with the head. center drill, then drill and tap to 5/16.
Nothing hard was ever easy but it is doable. Brake boosters, master cylinders, etc.. will be moved out of the way. Motor mounts unbolted, and engine rotated sideways to get a better angle on the dangle, whatever we need to do is what we do.