Well, here we have it.
The noise is still unknown and has NOT returned since I mentioned it originally. All nuts and bolts are tight with the exception of two. One nut and one bolt on the driver side exhaust manifold managed to back off of the flange. This has caused an exhaust leak and I can not get either the nut, nor the bolt, to budge to save my life.
My solution is this. Since I still don't have the pistons for the lightning engine, I'm going to find a PI 4.6 intake(a damn cheap one I hope), and do the PI top end swap on my 185-6k NPI bottom end. That way I can put my ported exhaust mani's on that have GOOD studs. I know you may think I'm crazy for upping the CR on such a tired bottom end, but I have faith in it. Not only that, but I'll have a backup daily driver in case I DO blow it up.
This will at least get rid of one pair of PI heads I have, along with some other stuff I want to use on the 5.4 but can't yet(it can all be pulled off the 4.6 and reused on the 5.4). All of that stuff can be acquired again though. Guess I'll start porting the second set of PI's so when I actually go through with the swap, it'll be quick and painless.
That's my story and I'm sticking to it. Is it the best plan? Probably not, but it's a plan. As a friend of mine said in the past, "Make a decision, even if it's wrong!"
Hell, if I get inclined enough, I'll get a set of rings and put the set of used lightning pistons in that I have as well. It'd bring the compression down though....