/6 advice

It sounds like you did everything but a valve adjustment. Those engines have solid lifters in them and it's quite possible that you have a tight valve. Or there could be some surface rust on some of the valve seats from sitting over the years too.
Pull the rocker cover off and check the lash. I think they call for .010" int. and .020" exh. and it should be done hot while running.
If this happens to help you will likely have to readjust them again after you put some miles on it and the crud burns off the seats.

Ted