Yes, it definitely is and I've done it that way but when there is a small pinhole leak somewhere, the bleed-down is so slow and gradual that it is hard to discern whether the leak is from a hole or if it's from what I'm using to seal off the header. I've found the most effective way to detect leaks is to pressurize the header with air and submerge in a big tub of water and look for the bubbles. But you are right, I could test the way you're suggesting and then if there is a leak, I still have to remove it and test in the tub to find the leaks. I'm just trying to make my life a little easier when re-installing them.

Yeah, that is my suspicion as well. I have an old header at home, so I can at least test the nut clearance and I can probably stand the header up to simulate it being on the engine and see if I can get the socket in there and whether the angle on the socket extension is feasible when it's between two headers.

Back when I was hot rodding, I've heated many a header tube to dimple it and gain access for a socket. ...can't really do that with boats.

OK, so I took an old header and test fitted the studs and the flange nuts and there is definitely enough room between the bolt holes to allow both flange nuts to seat properly. But this header is for my center engine and has fully upright tubes, so what I can't tell from this is whether I will be able to get a 9/16" socket in between the tubes on the swept back headers.

use a 12 pt jet nut. they are 3/8 thread but use a 7/16 socket. that is what I used on all the race boats with all of then studded.

Thanks for the suggestion. those things are expensive...

ARP makes exactly what you looking for. SS studs with SS locking nuts in 6 or 12 point. I used them on my Pantera.

I've found the nuts, any idea on the part number for the studs?

Never mind, I've found it.

post up what you're using, I may switch