Thanks for the great reply!!

Thanks Capt.  I'll check them out!

I'll see if I can get a pic of the lifters...not sure who makes them.  We talked to a tech at Erson today.  He said to try up to 1 1/2 turns and see if that helps.  We'll try that next week and I'll report back.

Not sure of the spring pressure.  I'd have to find that out from the builder.  We talked about it and he said it wasn't excessive.  I do know he checked the spring pressures on his second time through the motor to make sure they are actually what they are supposed to be, and he said they are.  We have gone as far as a full turn as an experiment and no change.  Dead quiet when she's cold, and horrible once the oil pressure drops to about 40-45.  The builder and his contact at Erson designed this second cam to try to solve the problem.  It's very mild.  There seems to be plenty of oil up top....but to be honest, I can't say if I noticed a change in the amount before and after the clatter starts.  We are going to run it again either this afternoon or Monday.  I'll look for that.  I feel pretty confident the oil pressure reading we are seeing is accurate...it's been on 2 different run stands and a dyno and had several different pressure transmitters....and all the different readings are within a pound or two of each other.  This is my first post and it's awesome to hear the ideas.  We're all stumped, so hopefully with some help we can get this thing figured out!

I should have provided more detail the first time.  Sorry about that....new to the forum thing.  The engine was totally rebuilt by a professional FE builder/restorer with 35+ years at it.  The block was completely worked over at the machine shop, and the oil passages were supposedly checked, cleaned, and enlarged to accommodate the larger oil pan and high volume oil pump.  The pressures are at idle....70-75 cold and around 40 hot.  It currently has an Erson cam and lifters, and T&D rockers.  An important thing I forgot to mention....on start up and until the oil pressure reaches about 50-55 psi, the engine is dead quiet.  She sounds like a fine sewing machine.  Around 50-55 psi, the annoying clatter starts....and once we're down around 40-45 psi, everyone starts shaking their heads and running for cover.  If it sounded hot like it does cold, I'd be thrilled.