I've got the head off my D16A6, it's all shined up, surrfaced, valves have been re-seated, the whole shebang. But, I'd also like to possibly open up the valve faces a little bit. Is this something that requires valve removal to do? Will it help improve flow? There are some pretty big flanges sticking out over the valves faces, so I think opening that up will help a decent amount.

Any info is appreciated, I'm probably going to have the same shop that cleaned the head up do the work, since I have zero experience working with heads, let alone grinding.