Quote Originally Posted by Johncockrell View Post
I used a 1/2 by 13 tap to clean the threads on one side of my 6.5 block before I found out they were metric. Are there 1/2 by 13 head bolts available for this engine. A 1/2” bolt will go through the head.
Bummer... I don't have a suggestion for you, except for maybe installing inserts to allow using the correct metric bolt thread/pitch. An engine shop near you might have a better solution, or be able to install the inserts for you.

And, our Troubleshooting & Repair Guide specifies what tap to use. This Guide is not very expensive... See my signature below. It contains the best info you'll find anywhere for replacing head gaskets correctly, and lots of other parts.