As long as the valve gets lifted properly, the shape of the cam follower doesn't make much difference to me. The later style might be a little lighter, but at the normal RPM range for a stovebolt engine, I don't think it makes much difference. The milk can shape is just a holdover from the 216 design, in my opinion. Once hydraulics came into common use, I think "solids" got redesigned so the same length pushrods could be run in either type of engine. Some of today's mechanical lifters are simply hydraulics without the plunger and check valve installed- - - -just the pushrod seat and a spring clip.
Jerry
