That is a big engine so it will have a lot of blowby and that long stroke will stir up the oil in the pan. So no surprise that you're having oil blow out the breathers.

One thing to try is high quality breathers such as the ones that Peterson makes. They screw into a #12 bung so you might need to weld bungs to your valve covers. The other thing to try is to put the breathers on a remote tank. On the dyno I use a two quart Moroso tank with a breather and then run a line from each valve cover. That setup never leaks a drop and it doesn't blow out any oil. I've used the same type of setup in a car by mounting the breather tank up next to the radiator. I'll attach a couple of pictures.