This. Many B&S engines have the plastic composite camshafts anyway. The most important thing with these splash lubricated engines is keeping the oil level full.Do you realize how little valve spring pressure an OPE engine actually has? This whole zinc thing is way overblown for OPE engines.
Just because modern PCMO lack ZDDP doesn't mean they aren't great at lubricating, other additives are used in place of ZDDP. The cheapest oil you can find at WalMart or any auto parts store with an API certification is better than what most manuals recommend anyway. I bought a new Toro mower this past year, and the oil recommendation in the manual basically stated any oil meeting/exceeding API certs from the 1980s was sufficient.