Yes you need an additive, although with the spring pressures associated with a slant 6 I don;t think you have to be too concerned about which one.
Comp Cams additive (from what I have heard) is actually a megadose of Moly, not zinc. I don't know about Lucas. There are some oils that cater to our concerns (Royal Purple, Amsoil, Redline etc) by purporting to have plenty in the bottle already. Diesel oils are still ok (Chevron Delo, Shell Rotella) but they do have much less than they used to, and are likely to continue to decrease in the future.
ZDDPlus (I use it) is a Megadose of Zinc and is available from Ebay, Eastwood, or direct www.zddplus.com
Even STP red has about 4000ppm (you want at least 1200ppm in the pan, the "energy conserving" regular oils on the shelf can only be trusted to have 600-800 ppm.

Do a search on Zinc, you will find lots of info