Have ypu taken the issue with Ron Iskenderian? Perhaps if you sent the failed
lifters back to Iskenderian, they might be
able to shed some light on it such as the
lifters failing from
oil starvation. Needless
to say, if your engine setup is providing
good pressure to the galleries, it may
not be providing sufficient
oil to the lifter
bearings. Galliing of the needle bearing
roller assemblies would seem to be due
to insufficient lubrication, valve spring
pressure beyond what the lifters were
designed for, or excessive camshaft "walk" that could cause uneven loading
of the lifter rollers.
.....Fred