I know this has been posted before but I would like to make sure it is still Accurate. Specs for stock Cam Lash is .019 in the Ford Shop Manual. Equivalent to 90 degree counter clockwise rotation of the Adjuster Screws from Zero Lash ? This would apply to worn Rocker Arms where the Feeler Gauge would no longer be Accurate?. Is .019 still considered to be correct or is .020 or .021 more realistic because of changes in material used when these Engines have been rebuilt over the Years?