I am getting ready to change the oil for the first time on our 1968 firebird, has a re-manufactured 1969 6.6L 400 under the hood. TH400 transmission. I am looking at Jeg's and Summit to buy oil. They are recommending 10W30 Red Line synthetic and a host of other oils that are "racing" oil (i.e. Valvoline Vr1), summit even has a semi-synthetic Penn Grade oil listed. Any suggestions? I do not race. This is a convertible that my wife and I drive whenever the weather permits (no snow or ice, or hopefully rain). I prefer putting in a high quality oil, just was skeptical of putting a synthetic into an older engine.

Thank you in advance for any recommendations.
Jake