Bajapred, you hit the nail on the head. I am seriously an overthinker/worry wart when it comes to this type of thing. The motors are a big investment, just wanna not regret it later.

Those early style two piece CMI headers had a reputation for being strong and leak free from what I have been told. Innovation used quite a few of those sets on the high speed special forces craft they built for the Navy on those big 632 cubic inch mills they produced. a I know they were beat on pretty badly in actual military use and I don't believe the military had a real problem with leaks in them. I think their shape and strong tube routing made them stronger than current tubular headers.
( Maybe less prone to vibration damage)
However that being said, testing before using is a smart way to go and I prefer to use compressed air and submerge the header underwater to find cracks and leaks. Seems to be a better way to find any possible weaknesses and leaks than using water.
Just my two cents.

Best Regards,
Ray @ Raylar

So if you tested them with compressed air and they passed you would feel comfortable using them on new motors? They've been sitting for 10-12 years and have approx. 150 hrs give or take a few the guy says. This guy keeps his stuff in tip top shape. He had 680 hp motors. He pretty much told me what you just said minus the military part. The engine builder was concerned with them being discontinued , if they were such a good design, he stated that there are many more welds to crack on those compard to the new style. but they seem to be built extremely well. He also uses compressed air to test his header in a tank opposed to the garden hose method.

If those headers were stored dry and they test good I would have no problem using them as long as you properly apply them to your boat with good tails and such and remember to flush after salt use and drain and store them dry and empty during winter layup. I would recommend testing them for leakage every two years or so depending on usage hours and boating conditions.
As for discontinued I don't see how that even matters as if in the future you need to replace the system you would probably opt to replace all and start fresh.

Best Regards,
Ray @ Raylar