Technical Flathead Lifters/Tappets - Adjustable vs non-Adjustable

Actually found an old thread on here which mentions the mushroom head valves were designed as such due to the the thinness of the factory stock non adjustable liftets. The idea was to spread the forces over a wider area which makes sense.

 

So are stock lifters for late flattys thicker on the top casting to withstand the huge downforce and concentrated impact point the sharp later valve will have?

 

Finally got around to ordering the lifters from TopLine. Great service. For future ref, P/N is B-2032 (tray = qty 16). Block should heading for cleaning this week, and finally some machining. Good to know product is top quality and made in the USA.