Have you tried the
oil restriction techniques to the vavle train described in many postings ? You would have to remove your rocker shaft assemblies ( both sides). Under one of the middle rocker stands (one on each side) there is a small hole that feeds
oil to the rockers from the cam. Insert a short length of rod ( about 3/4") with a .090 hole drilled through its length into this
oil feed hole. This will restrict the oil but will allow enough through to oil the rockers. This technique is also described in Pat Ganahl's book "Ford Perfomance".
Paul