When you've replaced the guides you do usually have the seats recut for a couple of reasons; Firstly if your old guides were excessively worn the seats will have been worn too (not by a lot but it is measurable) because of the stem moving about in the guide. Secondly the chances of the new guide holding the valve in exactly the same position as the old guide is virtually nil and the valve won't seat correctly as it's off centre relative to the seat.