... if you are sure you have the valve timing set up right and you didnt somehow bend the valves after install of the head, rings are good and head-gasket is sealed.... the isnt really anything else but the valve/lifter problem. Do a leak down with the cams out.
There werent a whole lot of 16v's coming through the shop I used to work at but still a few. I never heard of any problems after sending a head to the machine shop.
1972 Volvo 142e
1983 Volvo 242 turbo 16v
1995 Volvo 850 T5R