I put my stock endlinks and mounts on the STi bar. The parts in my hand is what came off the STi bar.
Difference in size.
I started to size up the rear STi sway bar by replacing the Legacy torsion bars with the STi ones (these fit fine). I checked the length of the Sti sway bar and it also looked like it will fit (I will know for sure later today when I do the rest). For this to work you need STi torsion bars, STi rear sway bar (duh), STi rubber bushings, STi endlinks (these work with the STi torsion bars), and Legacy metal sway bar mounts.
To hang the STi sway bars I had to use the STi rubber bushings with the Legacy metal mounts (STi bushings fit the bar, Legacy mounts fit the car). The STi rubber bushings have a lip so to make them fit the Legacy mounts you need to grind the lips down like so.
From there I could mount ONE side (you will see why I said one in a second) of the sway bar and test fit it with the STi torsion bar.
Now the reason I could only mount one side is the spot where you put the spare tire is in the way. I started to cut at it tonight and I'll finish it today.
Hope this helps. I will update this when I get further along. Not sure how far I will get today with the Superbowl going on.