Odd capped head at coolant crossover.
 

Picked up a set of 16s to use on my street car project. Took the 2nd set apart to go through them and noticed a freeze plug installed in the water port on the passenger head at the front crossover. Driver side was open. So what was the builder/head guy motive to do this? Only history of the head is that it was on a 68 gto, original to that car, and then went to aluminum head and guy passed away. Friend of his I bought these from dont know.

Are you sure you don't have two drivers side heads?

Really Paul, I mean really?

Okay I'll play..... Why ? :D

Because they were worked on by a shop. They had epoxy in the bowls to make a wing, ported some. 45 exhaust seat, 30 degree intake seat. Was set up with 995 style springs. The pass head has the nipple in the rear of head and the front plug is not close to flush. These were on a running car before they came off. The nipple in the rear is new. So there was somebody in there who did the engine over too.

Well, since you don't like my questions I'll tell you my thoughts from your provided information. First off the heads probably didn't work that well. Secondly the "new" nipple fitting might be the key to answering your original posted question. Third, I'm sure you will be able to get those heads to work for your intended project. Fourth, I would remove the plug at the water crossover to allow the water to flow freely.

Maybe a NON Pontiac machine shop worker put that plug in by mistake???
Pontiacs are different animals. Pontiac engines/heads have been out of the main stream for general machine shop work for at least 20 years...
Thanks, Paul!!!

Maybe that's why it was severely over heating and he switched to aluminum heads because aluminum runs cooler and all along he was thinking it was running hot because the heads were making so much more horsepower and horsepower is heat!

Apparently its a bad-aid or "cover". Found a hole in a port under some moroso epoxy. Figured he would cap it for I dont know why. Hole is right behind head bolt center divider in the water. I just opened up the hole and back filled the jacket between the 2 ports with splashzone. About a golf ball amount. Sent a rod from deck hole to cram it all against the head bolt boss from top of head to deck side, and forced between both intake bowls. Gonna add some white elmers glue gunk through the water jacket and gonna send it.

Probably cracked because they overheated the crap out of that head because the water crossover was capped.... All that and they thought they were making too much horsepower!

So the plug might've been used for leak testing then?

Not a crack. He ported bowl thin and went through. Probably put cap in thinking it will help from blowing out.

Was it ran with the cap in?
Was it installed for pressure testing?

Ran with cap. I took heads as they came off car with spark plugs in and residual oil around valvetrain