I have seen lots of heads with the valve guides ground flat. I think there is a big advantage in raising the ceiling of the exhaust bowl which requires grinding the valve guide flat. My head builder however said that the gains in removing the valve guide that sticks down is not measurable and the extra stress it puts on the valve is not worth it. So after I ground the bowls the way I wanted them, he put new guides in.
Be careful around the valve guide in the intake bowl. You gotta keep the shape which creates "swirl" around the valve. If your dumping air in straight and the valve shuts, it messes up the momentum. But if you have a swirl effect, when the valve shuts, the air just swirls around the valve until it opens back up again and then it goes around the valve like a toilet flushing. Looks good so far.
Another tidbit of advice, I would not recommend opening the exhaust port at the gasket. It is already much larger than the bowl volume. The best thing on the exhaust would be to try to enlarge the bowl volume and even the velocity throughout the port.
There are also big gains easily had by unshrouding the valves. Just pop in some old valves so you don't damage your valve seats and lay back the angle of the wall which is currently shrouding the valves. Just make sure it's the same in each chamber and that you don't go outside the diameter of the cylinder.