Bruce, you always make me think hard about stuff.    No code radio licenses.   Post-open software licenses.   Now zinc vs copper anti-sieze!   At least this time there are no lawyers involved :-)

I have experience with several New England antenna builders who swear by Jet Lube SS-30 copper anti-sieze, and I have personally disassembled 20m yagi elements that had been exposed to 7 years of New England weather and they came apart just fine with no evidence of corrosion.    But now that I think about it, the fact that it had some kind of anti-sieze/anti corrosion grease applied was probably the critical factor, with zinc or other fillers possibly working just as well as or even better the copper.

Permatex explicitly recommends their copper based product for use with spark plugs in aluminum heads, although I will concede that there is not a lot of moisture involved in that specific application.

No matter what metal is in your anti-sieze, make sure to wear your oldest work clothes when you use it ... that stuff gets everywhere if you are even the slightest bit sloppy with it,  and it stains your clothes permanently.   

de KM1P Joe