Quoted from pinengineer77:

I should also mention that the mechs fit as-is on the lower PF without any modifications. However on the upper PF you have to move and re-wire several light sockets to make room for the mechanism. I think I also had to grind away a small section of the mech for clearance but this was long enough ago I don't recall the details. Just letting you know the upper flipper will be more involved than just centering the mech and bolting it in.
Also to center the mech, I took a clear plastic sandwich bag and cut a ~1.5" strip of plastic and wrapped that around the flipper bushing and then inserted the mechanism into the PF using the thickness of multiple wraps of the plastic bag as a spacer to center the mech. Then I bolted the mech into the PF. Very important to have these perfectly centered or the geometry or flipper distance will change.
I also used the WPC unmarked flippers from Pinball Life in Yellow. Don't like the looks of the fat tipped Ballys - just an opinion, YMMV. The before (original Bally linear) and after (WPC conversion) flipper tip to tip was within 0.03" from my recollection, within a margin of measuring error.