[Kahuna]

Ok, before I go any further, I should say that if and when I do another flathead engine, I would NOT use adjustable lifters. I just don't really trust them, especially in an engine that I've invested a large amount of time and money in.
Fourdy
Lash caps are items in varying thicknesses (like .060", .090", etc. they do not screw on, but rather are a very tight fit to the valve stem. They are hardened steel. They are used regularly in high-performance engines. They are available from places like Jeg's, Speedway, Summit, etc.
In my opinion, they are a helpful item, but are just another bandaid.
Jim