I had one of these new ones installed on my bike a week to make sure the length wasn't a factor. Everything seemed great with the longer lever length.
The directions for installation were posted above and are still correct. Some things to notice for installation:
Make sure the cable isn't binding by resting on top of that cover bolted to the top of the transmission. It should rest to the side of that thing.
Make sure the handlebar adjustment is tightened all the way in and all the slack is out of the cable and make sure you turn the splined shaft clockwise until it stops before you try to slide the new lever on the shaft. If you don't do this, it will be on the wrong spline and the adjustment screw will max out before your handlebar lever is all the way out.
Now is a good time to lube up the cable.
I'm pretty sure you can pull that rubber boot through the hole on the mount. Mine was rotten and falling off by itself so I didn't give it a try. It's been exposed for years now and the clutch still feels good.
It may take you a couple tries to get the lever on the right spline. Just be patient and don't install the circlip until you get it right. You'll know when you do when you can adjust the handlebar lever until there is no slack left with the adjustment screw.
You will have to re-learn the clutch! :BLAA:
Give it about a week of riding and you'll probably never go back to the stock setting. The pull will be much lighter and the friction zone will be much longer than you're used to.