Well consider this, the lift and durations are the same for the intake valves, but different for the exhaust. That could 'splain the difference between the two. It's a remote possibility.
Jusy because the lift and duration are different or the same does not mean the the studs have the same amount of friction holding them in..... If you need adjustable rockers then you need screw-in studs.
The difference in height is probably from the lash caps he has on the valves. I have converted a few with hardened washers and aircraft nuts, if it will work on Chevy's from the factory the should work on a Ford.
