Oil recommendation for my 1970 dodge dart with 318 engine

no need to run 10 or 30 W oils anymore
used to be you had to run a lot of anti thin out additive which sheared down so 10W30 or 20W 50 made sense if you needed a 30 or 50 wt oil
not any more
the new base stocks do not shear down much so a 0W oil can be built with almost no additives
Made out of Natural Gas
a 0 W oil cold can be the same viscosity as a 40 hot
or you can actually have an oil that is 40 hot and still flow well when cold- and even Texas is "cold" as far as oil flow is concerned
anything else you have to preheat your oil
run full synthetic 0W 40
look at the Oil for the New corvette as an example
or if you need a 0W-20 look at the VW 508 spec oil