FYI: The oil companies made a change to the formulation of oil not too long ago.
Basically, anything that has that starburst on it that says "For Use in Gasoline Engines" doesn't have nearly the needed amounts of the ZDDP additive in it that helps reduce engine wear when the oil starts to go after 1500 miles or so.
You will want to be careful if you have the "Flat Tappet" type of cam -- and virtually all of us do, whether we're talking Stovebolt 6 or SBC/BBC. Without ZDDP, the lobes on the cam will end up wearing down, and then you will need to replace it.
Newer engines (post late 1990's) will have a "Roller Tappet" type of cam, and these can take any sort of oil that you can throw at them. (For instance, my 3800 V-6 in my 1999 Pontiac has a roller tappet cam, and I use regular standard-issue 10w30 oil in that.)
The reason the oil companies reformulated the oil a few years back was because the Automotive companies asked them to. Aparently, they're supposed to be warrantying the catalytic converters up to 120k miles nowadays, and the phosphorus in ZDDP buggers up their innards substantially short of that, and if you've ever replaced one, you know they aren't cheap.
Diesel oils still have the additiive (Rotella T, Delo 400) and so do just about everyone's racing oils (Valvoline's VR-1 comes to mind). The easiest way to make sure is to turn the bottle over and read the fine print on the back. Look for the ILSAC GF-3/GF-4 ratings on the back of the bottles, and the aforementioned "starburt" on the front. If it has either one, put it back and reach for something else.
This is an across the board change on both "Dino" and Synthetic oils. Whatever you do, make sure you've got the the right stuff, or you'll end up like Beaver 53 with 3 blown V-8's in 3 years.
If you can't find anything that has ZDDP in it, go to your GM Dealership and ask for a bottle of the engine break-in addititive -- I think they call it Engine Oil Supplement. It is, according to several forums, pure ZDDP, and will augment your oil nicely.
STP has 2 types of oil additives that might work as well. The blue bottle is ZDDP and Paraffin, which I will never purposely put into my engines, and the red bottle is supposedly just ZDDP, but I have yet to read this in more than one place.
