[Rick Parker]

Generally speaking the cause for this problem is that most of the aftemarket heads use Chevy (oops) length valves and springs which leads to a a taller installed height along with a change in the geometry. It pushes the valve stem side of the rocker further up towards the roof of the valve cover. Combine this with the various heights of the valve cover/cylinder head gasket mating surfaces relative to the top of the rocker arm and you have the recipe for a real headache. Just do some careful measuring, even with clay (similar to checking valve to piston clearance) if necessary (do this on a cold non running engine) and determine what clearances you now have and what you need. There are some tin covers that will fit many roller setups. They have
"Powered By Ford" stamped into them, mid to late 70's stuff.

Rick.......