Zinc Additive for Flat Tappet break-in?

ramcharger said
Arrrrrgh! I wonder why? EPA jumping on their backs?

I believe it is still made under the AC Delco name.

I have heard that the STP in the red bottle has a decent amount of zinc content in it to help. Is this true and is it mixable with synthetic oil?

Also, I have 1,500-2,000 miles on my newly rebuilt 318 with comp XE268 cam. Is this too early for synthetic oil?