I've been contemplating a LS nto an older hot rod and was noticing a lot of discussion about broken valves in these motors( afreind has an alum block/head motor out of a caddy that broke a valve stem at only 21000 miles). Is there a problem with the materials or is it because of the 8mm stem size? I'm thinking about L92 heads but dont want to buy complete heads if I'm gonna replace the valves and springs anyway.

 

It is from people overreving (often a missed shift) and floating the valves and/or too little PTV with a big cam.