Most of them are a bolt-on. Just put them on, adjust, and run.
Many people insist on using longer studs for the locking nuts, but it depends on many things. I've never had a problem using them on stock studs but it could be a coincidence that I had the right brand of lock nuts or something.
You may also need tall valve covers or a spacer, but many small blocks are just fine with stock covers. There again it probably depends on who's locking nuts you're using.
Centerbolt valve covers require a special narrow-body rocker.