Too much air pressure on valve cover breathers

Hi:
I'm just finished the rebuild on my stroker small block, but in the first passes, after proper break in, when I rev up it blows a lot of air and oil thru the valve cover breathers ( real mess) ; Obviously something's wrong,
Everything was new, my builder says he cut the first ring to. 024 and the second to. 028, flat top forged Icon pistons, Hellfire rings.
Any toughs?
Thanks in advance