The rocker arms themselves may have been the cause of the lowered rpm for valve float.
For all their apparent weaknesses, the Mopar stamped rockers have a very small moment of inertia around the shaft centerline. Other rockers have higher moments of inertia and require more spring to make up for it.
Article by Dulcich or Freiburger years ago on a smallblock where they switched from stock to roller rockers and promptly lost 200 - 300 rpm.
