When you adjusted the valves did you find zero lash and then give the adjusting screw 1 1/2 turns tighter? With that much oil coming to the rockers I doubt there is any air getting to the lifter. I had a 1956 Chev. with a 235, one time that would have a bad valve noise after it got really warmed up on a hot day. I found out what caused this was the bore where the lifter ran in was worn just a little and when it was really warmed up there was too much clearance around the lifter for the oil pressure to pump the lifter up. I ended up putting in a solid lifter in the bore and adjusting the valve with the proper valve lash. It was that way when I traded it off many miles later.
