what kind of oil for new rebuild

OK gentleman lets talk real life. I've been running Mobil 1 5W-30 and 10W30 in my family vehicles since 1980 with no problems and will continue to use the oil. I was told back in 1995, in no uncertain terms, by the GM service manager not to use synthetic oil in my 5.7 liter 1/2 ton truck until I had 10K miles on the truck. GM's reason was that the synthetic oil "sometimes" hinders the piston rings from seating because it's to slippery. Yes Ace I used the word slippery. That precaution is no longer used by GM and as a matter of fact quite a few vehicles are coming out of the factory with synthetic oil already in them like my new Honda Accord.

Terry