Al,
Sounds like you have a very nice engine that was well designed.
I can't find any fault in your part selection and the only suggestion I can offer is to attempt to tighten the valve lash as much as possible. .025" is a bit loose for a street car. The issue is when the roller lifter is on the heel of the cam, the lash allows the roller lifter wheel to stop rotating. Then, as the cam comes up on the ramp the roller wheel literally slams into the lobe
and slides a bit before it starts rolling again. This action imparts an extreme impact shock on the needle bearings in the lifter, causing premature failure. Setting the lash as tight as possible will keep the wheel in contact with the lobe for as long as possible and hopefully keep the wheel constantly spinning.
The Isky Red Zone is an excellent lifter and is pressure fed to the lifter bearings. Isky may have had some weird manufacturing problem that caused your lifters to fail. One other consideration, although not very likely is the possiblity that the Royal Purple
synthetic oil is so slippery it is causing the rollers to not rotate on the heel of the cam but instead to slide untill the lobe smacks them again when the ramp starts to raise the lifter. I'm reaching now, but I can't find any other faults in your engine.
HTH,
--Mike