The lifter bouncing because of too much clearance is probably a good culprit.
I run a "rev Kit" which is some very light springs under the head.. between the head and the lifters, which keep the lifter in constant contact with cam...no bouncy bouncy!! This kit allows the use of very low valve spring pressures because the valve spring has only the valve to control. Imake sure that I blip the throttle constantly at idle to make sure the
oil is getting to the lifter wheels...I idle at 600 rpm and redline at 8000rpm...
John