I have a 350 SBC in my street rod and after it sits for a couple of days I get a real clattering from one lifter that goes flat. It goes away after a few minutes (3-5 minutes). I have changed the rocker nuts as one of them would not stay set and would loosen up and start the clattering again. There is really nothing else wrong with the motor. I run about 55lbs oil pressure when driving and about 30lbs at idle. My question is; is it feasible to change the lifters, push rods, rocker arms and nuts on a motor that you are not sure of the rest of the internals or the mileage on the motor. It burns no oil and does not leak.