Mopar action this summer mentioned 33-35 is sweet spot for power on a big block. I had found 34 worked best years ago. One time I had the distributor out, it bumped to 33 when I locked it down. I left it there and noticed no difference really so I’d vouch for their numbers.

Mopar used to say in the speed books that you should run 38. Back in the 70s you probably didn’t have a problem finding better fuels. I tried 38 and I got .5 mpg better, but it ran rough. I think it was signs of pre-ignition. Backing it down, that stock 383 hp smoothed out at 34 and was the smoothest engine I’ve ever had. That one was all factory built when I tore it down for a new chain and seals.