As promised here is a picture of the base of an F3. It is the same size tripod mount as on the EX1R, plus an additional off-set 1/4 hole towards the rear of the base (which is flat).

Below is a picture of the lens mount with the PL adapter removed. I was surprised to find that this appears to be the same mount as the EX3 except with the electrical contacts in a different position and a small pin in that locates with a cutout in the top lens mount flange. It looks to me as though an Adaptimax or MTF EX3 to Nikon adapter would go directly on the F3 with just a small slot cut in the top flange of the adapter to clear the extra mounting pin.