I put a fresh 455 olds Into my 56 Olds. rebuilt C Heads a fairly mild Lunati Cam (think performer RPM). I did not confirm the oil galley plug at the back of the block, Or that it had the tiny hole in it (an Olds Thing) There was a little flash rust in a lifter bore... the lifter went in but it was a little tight. Upon fire up, that lifter never pumped up, so i tore the Intake off and changed that lifter... the Cam looked good, so did the new pushrod and the new rocker assembly. NOW the same lifter is having problems...so... I am thinking the lifter is an effect not the cause. Is sounds OK at 25 mph (under 1500 rpm) but over that say 45 mph the lifter seem to collapse, hard throttle it collapses, after a a block at 25 it seems to quiet down. Seafoam helped a bit but didn't cure it. I really don't want to pull it back out, but I think i may have to. any ideas?