Chris, I'm sorry that was a bad joke. If you are talking about the sensor holes that go into the exhaust ports, I don't have any six heads with those. The 153 four cylinder I'm building has them but the head is not here right now. I looked online and through Leo's book and could find nothing. My 153 had steel alen head plugs in it when I got it. I replaced them with brass and am pretty sure they are pipe thread but not sure of size 1/2,3/8,5/16? I did read that someone plugger his Mustang head with an 11/16-13 bolt 1" long with two washers & sealer.. I don't know if they are the same.
