This whole thing is a long story no one wants to hear, so sorry for the long post. I replaced the lifters first with new ones. It quieted it down for the most part. Then the noise came back big time, tore it down to check preload - bleed down tool and all -found #1 exhaust way high in bleed down gap - then checked others and the exhaust's gaps were all higher than spec, but the intakes were within limits.
#1 Exhaust turned out to have a wiped lifter and cam lobe - that's why the gap was so high - bottom of lifter worn away.
In the process of putting new cam, lifters and springs in, I've been checking everything. The heads had unknown valves, springs and retainers installed. So I'm replacing all but the valves (maybe them too until this is done)
In checking for installed height, I find that the intake valves are too low - valve stem is lower than it needs to be - compared to E7 heads that were on the motor, before. The installed height is lower than specs as well - by the same amount - with the E7's I'm comparing too, right on spec.
I checked three more tonight and all of them are 0.019 - 0.022" short. I've been comparing installed height to 89 351W specs, so I checked the Explorer 5.0 specs and they are almost identical to the 89 specs (1.77-1.80) vs (1.78-1.81) I'm in the 1.55 range - too low.
Now I'm wondering if the intake valves are not the stock style valves and are less than the 5.70" specified overall length. Or are the spring retainers and valve locks different for a GT40P explorer motor than for a E7 truck engine?
I should just pull the head and measure the valve's height......
I realize a longer pushrod could take out the difference for the shorter valve tip height, but it might mess up the overall geometry a bit. Aftermarket keepers that are +.050" might raise the installed height of the spring within limit - but I just think something is wrong - these are stock heads that are supposedly equivalent to the E7's in valve train geometry.....
I'm really suspecting the valves as now I find each head had different valve stem seal styles on it! I know better - I should have pulled them apart and checked all this stuff first - so much for the quick bolt on upgrade...
Sorry about the long posts....