I used a bottle of Lucas Engine Break-In Oil Additive for the initial start of my engine, but I've got a roller cam so it was really not so much of an issue, just insurance.
http://www.lucasoil.com/products/dis...tid=9&loc=show
I've seen reference to GM's EOS Oil Additive, but others say that ZDD Plus has more than twice the zinc of the GM additive.
http://www.zddplus.com/
Initial breakin is critical, but if I were running a flat tappet cam I would be looking for an additive to add at every oil change. There have been cases where a cam lobe has rounded off in the first 20 minutes or so - scary!!