I think a complete valve job, surface mill/sand, and all new springs and guides are in order. But if you want to get by on the cheap you can lap the new valve in and call it good. Lapping is basically liquid sandpaper, grease mixed with grit. You put some on the valve seat, drop the valve in and spin it a bit until you can see that both the valve and seat have been sanded 360 degrees. You do not want to see a broken circle of sanding, that would mean that spot is too low and it will leak and burn the valve. It should take just a few seconds by hand. Be sure to clean all the grit out.