Might be a blown head gasket, valve seals, PCV valvesucking oil. Valve stem seals are a serious problem with ported heads. If the head porter cut the valve stems for valve seals, and used the stock exhaust valves then that is your problem. Stock exhaust valves NEED the valve guide un touched because there is a oil pump groove cut into the stock exhasut valve and NO seal is used. Alot of machine shops cut the guides for seals, thinking that they are doing the right thing, but in fact, they are completely killing any sort of oil control on the exhasut valves. The seal will end up riding on the under-cut stem (oil pump) of the valve, and not even make contact with this thin section of the valve. If the guides have been machined, then you MUST replace the exhaust valves with a smooth stem aftermarket stainless valve. No way around it. IF this is your condition, you should talk the machinist into machining/fitting the new valves for free. He made a mistake.
Plug your PCV valve for a week and see if it clears up. (leave the PCV valve in the manifold base, and plug the hose.)