The AS-4, AS-7, and AS-17 are the shoes for the F3. Another option, if you must have the bubble level above the eyepiece, would be to pick up a DE-5 finder. That's the one for the F3P. It sometimes surfaces by itself. Get one, replace the DE-2 or DE-3 with it, then slide your bubble level into the shoe. Only warning - if you ever decide to use a flash, don't attach it to the finder. Couple reasons why. Firstly, the meter display shuts off when a Nikon dedicated flash is attached to the DE-5's shoe and the center contact is dead, so it won't fire the flash. Secondly, even if it did work, you wouldn't have TTL flash capability. On an F3P, F3 Limited, or the F3H, the hot shoe is essentially a permanently attached AS-4.
Anyway, the F3 is a pretty decent camera. It does seem a little less balanced than other Nikon cameras that are the same weight and size (Nikkormat FTn as an example), but I like mine, even if I don't really care for the meter readout in manual mode.
-J