ProComp makes a set of closed chamber heads, but i wouldn't recommend them for more than 200 lbs valve seat pressure. They come with 2.250 int and 1.880 exh valve seats. They will make over 500 hp with a .600 lift cam with the right intake,carb, and headers. Being a procomp dealer i've sold a few sets of these heads, but not for racing, also they only come on ovel port intake. and they are cheap.
JMO
Zip.
Sorry i was wrong ProComp does not make a closed chamber head.