Good point RB. I think the valve train is such a mess that it can’t work right. I suspect that the rocker is slightly holding the valve open when it should be closed and then letting it close just beefier it is supposed to open. Then it maybe slow to close, the rocker nose holding the valve open pressed on the retainer.
For the benefit of those in the future here is the link to the article about putting big valves in without modifying the heads to unshroud the valve.
Chevy valves in a small block Ford head
Yes. Before all of these aftermarket heads were available, this was a pretty common swap for early 289 - 302 and even some of the 351W heads. Both Ford and Chevy heads use 11/32" valve stems and are very close in length. The 1.94" and 1.50" Chevy valves fit nicely into the asthmatic early Ford heads. A little pocket porting and gasket matching goes a long way with this swap. The trick though is; you MUST un-shroud the valves in the combustion chambers! Bigger valves do NOT mean you’ll get more flow. In fact, you can actually LOSE flow by having valves that are too big and they become shrouded by the walls of the combustion chamber.
Not to beat a hunk of dead cast iron, but it was routine to back up nearly an eighth in that tight spot with a mill and fine hand. There were, for a while, 1.90 valves that were great going into an early 70s 351 head. You were even better off subtly unshrouding a 4V Cleveland intake valve back in 1970-75!