Quote Originally Posted by DarkMark View Post
Does the p90 pickup sit balanced on the apex of the curved surface with gaps under the screw holes?
No. You'll need to put some sandpaper (I'd suggest P180 grit) on the top of the guitar by the pickup hole, and rub the cover on it until the base has a curve to it that matches the top. Only sand until the base under the raised part of the cover is curved, not the 'wings'. There is a bit of flex in the plastic so the 'wings' should then sit flat on the guitar once screwed down.

I haven't any experience with archtop bridges, so don't know if they have different acoustic properties, but again, sanding down to match the curve of the top will give best results. The split bridge base is there partly to accommodate different radius tops without sanding, but it's always better to sand it and have the best contact between the bridge and the top.