Valve clatter

[RoyBatty]

HI all,
Just thought I'd mention a fight I'm having with noisy valvetrain problems.
Out of nowhere last week, as I pulled into the driveway home from work, I noticed that my valves were making a bit of noise.
So I figure, no problem, I'll just reset my valve clearances.
Well, I've been through that procedure at least three times now and the noise persists!
The engine sounds great when cold and runs quiet and smooth until it reaches full operating temperature.
Then it starts sounding like there is no oil in the cam box.....and they are both FULL.
Using the old solid rod stethescope method, I was able to determine that the noise was coming only from the INTAKE cam box.
I have, changed oil, drained and added a different weight, switched from Castrol 10W-30 to Castrol 20W50.
The cam lobes, "look" ok and there are no leaking gaskets.
I compared the clearances hot to my cold setup clearances and found that on average the valve clearances open up about .008" when the engine reaches full operating temperature.
So now I am going to swap out cam box assemblies with the engine out of a '78 that I have in the side yard.
My friend that has advised me on the maintenance of this car, feels as though the valve clearances are opening up too far when the engine is fully warmed up.
By the way, the oil pressure is running in the 50's on the factory indicator and there are no other sighns of lack of lubrication.
So, has anyone else had this issue? If so, where did the problem lie?

[So Cal Mark]

that's a massive change in clearance. You could have worn valve guides, how's the oil consumption? Do the spark plugs show signs of oil?

[RoyBatty]

Hi Mark,
thanks for the reply.
Installed a different intake cam housing and cam assy. Set clearances. All noise is gone. Must be a crack in the cam housing?
By the way, is there a difference in the cam specs from my '75 to the '78 that I took the cam housing from? Doesn't seem to be any difference in how it runs. Other than it isn't clattering anymore.