the sharp lip a quater inch in from the seat, the one you just rounded off, take it all the way out. measure the id of the seat - pretend you had a round cutter that was exactly that o.d. and you ran it down in the bowl a half inch or so
after you grind or cut the seats (and i narrowed mine some when i did, movin them all the way out to the outside edge of the intake valve face and almost to the edge on the exhaust. you are not supposed to go all the way on the ex cuz if you do there is a chance you could burn the valve. same with narrowing the seats - that contact patch is how the valve gets rid of its heat so i couldnt make em as thin as i would have on a race only motor) anyways, you take some lapping compound and lap the valves so you can see where they make contact with the seat. the compound leaves a grey ring on the valve face and this will insure that you are not backcutting into that portion of the valve. (just dont grind any of the grey away) on a 45° valve back cut them 30° to the seat. on a 30° face it is tricky (cuz the valve stem wants to run into the wheel of the valve grinder at much less than 25° or so) but you can can still back cut them, you just have to be real careful while you do. i did mine 30° on the face and 20° on the b/c
hope that helps
don
oh, and i dont like scotchbrite pads on deck or cyl head mating surfaces. hard to keep stuff flat when you are using a pad on a 90° die grinder. its just the head so you will be fine, but never use them on the deck (it has narrow areas (between the cyls) and will remove more material there than in the wide areas like where the pushrods come thru)
