Running pressure with mine is about 20 lbs cruise, but then is up to about 30-35 when really on it. It actually caused some head gasket seepage when it was raw-water cooled.

When adding heat, the pressure jumps to 45-50.

If it’s not leaking under those conditions, I’d say they’re good to go!

I think we’re 50 psi water pressure here but not positive on that. I used air because it was a lot easier to see/regulate pressure.

I thought about going with Stainless Marine manifolds as well but didn't want to have drill and tap the holes with the engine still in the boat. Does anyone buy used sets of headers? I replaced mine assuming they were leaking but they tested fine. I noticed my spark plugs were getting steam cleaned but wasn't getting any water in the oil. Turned out to be reversion while using silent choice.

Used headers have had some good value lately because of long lead times in ordering new.