Oil??

Going back to the original question, see the following page:

Chrysler Oil Recommendations - 1975 Chrysler Service Manual

For summer driving, you will be safe to use a 10W-30 or 15W-40 HDEO. A Heavy Duty Engine Oil will have plenty of anti-wear additive for a flat tappet valve trains and better detergency than racing oil for street driven engines. Excessively thick oils (like 20W-50) waste power and fuel and are only required if your oil is extremely hot. 15W-40 will be the cheapest option and the CI-4/SL oils generally have 1300 to 1400 ppm of phosphorus for maximum valve train protection.

I don't think it makes sense to mix your own oil unless you know more about formulating an engine oil than Exxon, Shell, Chevron, Amsoil, etc. If you want a 30-weight semi-synthetic, just go out and buy one (like Shell Rotella SB 0W-30 or Petro-Canada Duron XL 0W-30). Synthetic oils have a more constant viscosity over a wide temperature range which means they don't thin out as quickly when hot and don't thicken up as much when cold. AFAIK, only synthetics get a 0W rating.

If you're using Lucas, don't forget that you also get foamy oil at no extra charge:
What about Additives?