pushing oil out valve cover

Take a look at the inside of the valve covers where the breather tubes are. There is usually a metal plate that has a large opening on one side. That plate should be pointing toward the exhaust side of the head. If the valve cover is installed the other way, it can act like a funnel to the breathers. When I build an engine, I don't put valve seals on the exhaust valves and I don't get anything like the oil useage you have. So, I don't think valve seals are the problem. Keep us posted on what you find out, so we don't wind up with the same problem.