A bit of spare time has allowed me to test-fit the 9R swingarm into the 7R frame. I'm going by limited interweb information that others have posted throughout the years. I realize that with any of this stuff, "Your results may Vary"... so I've decided to check dimensions and weights myself, just to be sure what differences can be established. To start off in the area of weight:
zx7r swingarm -- 8.785 kg
zx9r swingarm -- 6.755 kg (this is the late model braced one)
Saves 2.03 kg or 4.46 lbs
zx7r 493 g
zx9r 269 g
Saves 224g or .492 lbs
So both together is 5 lbs.
The next step will be weighing the caliper itself, as the 9r caliper is a smaller, lighter, single piston model. There will even be a minute difference in things like the swingarm bobbins... the 7R uses massive 12mm bolts, whereas the 9R uses 10mm.
In terms of the fitment, the first step was to swap the "top hat/shouldered" spacers from one side to the opposite. So, the threaded spacer pictured is normally on the RIGHT hand side on the 9R. By switching out the seals from left to right, you can then move this to the LEFT hand side of the 9R swingarm, so it will work in the 7R frame. There is a special notch/saddle in the 7R frame to accomodate it. There was also some discussion about 0.125" needing to be removed from this to align the chain. I noticed that the 9R spacer similar to the one pictured was not as "tall" as the 7R one. Perhaps this would allow the sprokets to line up? I used the shorter threaded spacer for now... we'll see if more material needs to be removed. On the opposite (right) side of the swingarm, I found a spacer that fit UNDER the oil seal, which held it in place, and ensured a snug fit with the frame by spacing out that shouldered spacer enough.
Once inserted into the frame, I snugged up the pivot bolt to the 14.5 ft/lbs called for in the manual. The swingarm pivoted freely, so nothing is binding. I then attached the swingarm linkage.
Everything is still together only finger tight. With just some eyball guessing, it appears the swingarm might be angled down too far...? That would mean that the dogbones are too short. These are the 7r dogbones, and the 9r ones are even shorter. There are "lowering kits" offered, which are simply longer dogbones, which might bring the ride height back into spec. Need to get wheels on it first to be sure. The jacked up reasets might be monkeying with my reference point. For the record, the swingarm from pivot to front of the axle slots is 1cm longer. Not sure a rider of my abilities will notice...