Thanks for all of this info. The 5.8L Pro Boss has throttle body injection and has two fuel pumps - one low and one high and both have been replaced. I know the high pressure pump is electric and I think the low pressure is as well but in any event, it was replaced.
OK.... then that eliminates a mechanical fuel pump as being the source of the noise!
I would have thought that the mechanic that replaced the lifters would have done the check on the rocker arm and that the mechanic that just checked it out (he pulled the valve covers and observed that all valves were working and there was no sticking) would have done the same thing. I have been told that there was no adjustment on the rocker arm as the lifters are hydraulic.
OK.... some of the 335 series Ford engines offered adjustable rocker arms..... apparently yours does not!
Yours is the style that allows you to fully tighten the stud nut.
In theory, this properly sets the hydraulic cam follower's plunger depth.
In reality, it may not compensate for worn cam lobes.... if the amount of wear causes the plunger to become out of it's pre-designed range!
(this is rather hard to explain without going into great detail)
Look at the GIF file.
Note how the rocker arm adjustment controls the push rod depth which in turn sets the plunger depth to within it's proper travel range.
I guess this just goes to show there are mechanics out there that really don't know everything.
As far as a fresh engine, my wife has pretty much put the kibosh on that. We've spent thousands already on trying to get this boat to run properly (new fuel pumps, new relays, new lifters, new sensors) and it has fought us every step of the way. It's very frustrating because the interior and exterior of the boat are in perfect condition - unusual for a 25 year old boat.
In terms of expenses, I've always thought that with a clean and nice boat with good interior, good transom and stringers, etc......, engine troubles are the least of your worries.
Unless I can find a relatively inexpensive fix, this boat is history.
Questions (assuming that this a valve train related issue):
Is this by chance a roller cam engine?
Why did the mechanic change the cam followers?
If Flat Tappet, when the old cam followers were removed, what did the "cam lobe face" look like?
If the convex profile was gone, why did the mechanic NOT consider checking the cam specs?
If by chance what you are hearing is lifter noise (cam follower), it will be due to the plunger "topping out" within it's travel range, of which in turn creates excessive rocker-arm-tip-to-valve-stem lash.... hence a clicking or clattering sound.
The non-adjustable rocker arms prevent you from further adjusting and setting the push rod further into the plunger's cup.