What oil is best?

Brand of oil is a matter of preference. The viscosity should be the first consideration. Multi-viscosity will help fuel mileage and circulates faster upon start-up. So a 10w-30 or 15w-40 should be used instead of a straight weight.

Since you have flat tappets, it couldn't hurt to lean towards oils advertising extra zinc - for older cars. Some say that the newer oils are "ok" for older cars. Probably some of the same people that say that 10% alcohol in our gas is "ok" too. BS, or at least lean on the "safer" side.

Personally I prefer Amsoil and have seen the benefits and extra "insurance" it provides. But it's up to you to determine what brand is most feasible to use.

[ame]http://www.amsoil.com/techservicesbulletin/MotorOil/TSB%20MO-2007-08-08%20Flat%20Tappet.pdf[/ame]