Clois
If this problem started with a new manifold installation, go back and check everything from that point on. Just because it is new doesn't mean it aint broken. Definately would do a plug check, possibly when ever it was running was it missing, whichever side the steam was coming out of exhaust would be a good place to start checking that bank of cylinders. I have had seen problems of intake gaskets leaking water into an intake port before, usually you can tell, motor will miss, not sound right. Good news if any, no water in
oil , therefore the problem really should not be hard to locate.
DON