Rocker compatability question/Magnum

I have been reading up on rockers, specifically magnum rockers as LA rockers are shaft mount and unique. But I cannot figure out how to tell if a stud mount rocker arm is compatible with a certain head. Does it all have to do with the stud size...eg 5/16, 3/8 or 7/16?

For example: I believe I read factory magnums are 5/16 stud...if so, that happens to be the same as 3800 series II/III GM V6. Edelbrock magnum heads were intentionally drilled to 3/8 studs, which I guess was for strength. But 3/8 is pretty common, SBC, SBF; most companies have a 3/8 offering. If you look at parts lists, most suppliers list rocker arms by stud size rather than motor application, leaving me to assume that if you have the right stud size, rocker arms just bolt on.

Or is there more to it?