recommended oil for '68 383 ?

Any premium brand 10w/30 with a good amount of zinc will suffice. Since I am not interested in the synthetics, I cannot comment on their zinc content. I don't think there are many synthetics with enough zinc for flat tappets.

As mentioned already, the Lucas Hot rod & Classic oil is a good, quality premium oil that has 2400 PPM of ZDDP. I run it in my '75 F250 and it does very well. Holds good pressure.

Also, you need to be careful if you decide to use a ZDDP additive. First off, you need to premix it before you put it in the engine. Doing this makes sure you distribute the additive evenly rather than it sitting in the bottom of the oil pan waiting its turn to get sucked up by the oil pump.

Lastly, make SURE to read the label if you go with an additive, because there are several BS products on the market. READ the label Make sure it says it has ZDDP in it. There are some that say right on the label "contains no zinc of phosphorus". What the hell good is that?

Thank you drive through.