360 Exhaust Manifold bolts
 

Are the top holes for the exhaust manifolds threaded? Mine had bolts through the top with nuts on the back. I can't get a tap to run through them either. Thanks

Originally the head was threaded but the top bolts are very rust prone and sometimes people will drill them out and use a bolt and nut to clamp them together. The actual manifold bolt holes are not threaded.

They should have been threaded. I believe it's a 3/8" bolt. If they put a smaller bolt all the way through, it may have helped corrode the threads.