By the way, Shell Rotella T 15-40 oil, available in gallons at Wally-Mart, would be a good choice, too, for iron sleeved engines.
For the standard aluminum bore, or aluminum big bore kits, I'd probably go with one of the syn-natural oil blends, but would change it more frequently. I'd also go up as high as I could on the oil weight, especially in the hotter areas of the country.
Remember: the oil viscosity enhancing additives tend to break down between 1000 and 2000 miles, with the oil seeking the lower viscosity rating!
(This is why I'm a fan of straight weight oil, though the higher straight weights are getting harder to find at the auto parts stores. Heck most of them around here have even quit carrying racing oil. Bummer.)
