My Impala motor is in excellent condition but hasn't been run much in the past 23 years. I have 30W Quaker State in it now but there is some question about using modern oil in this 283. What is the preferred oil for it??

I would recommend a multi grade 10-W-30 detergent.

I will second that. The modern 10-30 oil is 100 times better than the 10-30 oil available in 1958.
A good detergent #30 is OK if you drive at high speeds in hot weather.