I have a 454 that was marinized by PCM in my 1989 Supra Saltare ski boat.
Ever since I purchased the boat last year it has been running horribly at
WOT -- this question is about something different however. Stick with me --
it may get long. I'm a complete amateur at this stuff so I'm going to
include everything I can think of and maybe someone can help me.

Beginning the other day the engine exhaust began smelling really bad.
People on the back of the boat were complaining of the exhaust fumes making
them feel sick -- the first time this had happened. Later that day the
engine developed a really loud clicking from the passenger side front of the
engine -- it became much worse as the rpms were increased. It was clear
that it had something to do with the valve-train so me and a buddy took the
headers and valve covers off, and found a rocker arm that was much looser
(had more lash in it?) at DCT. The valves still seemed to be fine, we could
actuate them by hand and they felt correct. The pushrod on that cylinder
was fine. The funny part was that all of the other rocker-arms were
tightened down on the adjustment studs the exact same amount -- to take the
lash out of this noisy rocker-arm I would have to tighten it down 2-3
threads further then any of the others -- this just doesn't seem right to me
that one rocker arm needs to be adjusted tighter then the others.

What would cause this? I've heard that the rocker-arm tightening studs can
begin to pull out and could have to be machined, and I've heard that I may
have had a lifter collapse. What is my next step to try and resolve this
problem?

Thanks for any and all help.

Rob