How big of a 4 barrel on a stock 1970 318?

Mopar Tim's 570 would work great. But anything around 600 would be an improvement. If you are good with carbs, a TQ would really perform.
I've had a few 100% bone stock 318 2 bbl's with duals, and always gained by going to a 4bbl. I usually held them to at least 4600 rpms, some 4800 rpm's with the duals and 4bbl and stock manifods.