Oil in exhaust crossover. Help needed

It's a 383
oil in the horseshoe almost HAS to be coming from the valve covers.
And the likely culprit is build-up of CC pressure, due to the improperly plumbed PCV System.
The PCV HAS to be plumbed to the PCV port on the front of the carb where it exits UNDERneath the primary blades into a a hi-vacuum area.
The breather on the other cover does not need to go to the air box, but if you don't plumb it there, it will puke vapors onto the VC at WOT, when the CC pressure builds up. Or you can install a breather with a big nipple on it and redirect those vapors.
In any case, if you do NOT route that breather to filtered air in the airbox, you will have to wash it out periodically as it does fill up with dirt and dust.