PLEASE HELP! Deep Engine Knock...Head Scatcher

[wild4wheels]

OK, 71 Longhorn 350. Had somebody that owed me money doing some "easy" work for me. I needed the valve cover gaskets and intake gaskets replaced due to some leaks.. not the only ones mind you but a good place to start.

It is a 63000 actual mile truck mind you and ran like a top in the summer months. Had some hesitation during winter months...another mechanic said that the valley under the manifold was plugged and need to be cleaned out.

So, this guy took off the valve covers, carb, distributor, coil, manifold, water neck etc....next day replaced the gaskets cleaned the valley..carbon build up on heads, reasembled and heard a loud, deep knockpass. side. called it a tick...no friggen way...it's a knock. He called a mechanic buddy of his over. and tried to pin point it. He told him to do it all over again..start over..maybe he had forgot something..did everything a second time...same thing..mechanic buddy came over again..adjusted some valves...thought it was the fuel pump..replaced that..STILL has the friggen knock. he thinks its now a lifter..ANY IDEAS? Prior to this I didn;t even have as much of a flutter of a lifter...I told him to count his sockets...dropped something in there? dunno..pulling what little hair I have left out...