I hope this is some help. I was communicating with the operations manager at Rideworx/Barkbuster last week about fitting Barkbusters either to my existing XTR bars, or to replacement Renthals. This is his response:

"The BHG15-01 will bolt straight onto a Renthal 7/8th bar. So no problems if you choose to go with this.

However, since this is the same kit that will fit the standard bars why not try to fit this way first.
You shouldn�t need to remove the inserts from the Yamaha bars because you can use the existing threaded insert as a mounting point for your Barkbusters bar end bolts.
I believe the thread is 6mm so you could have it drilled and tapped to 8mm or else you could find longer 6mm bolts.

Since you were thinking about leaving the original bar ends in place maybe your best way forward would be try the BHG15-01 fitted to your standard bars and bar ends but with longer 6mm bolts. (you will need something about 10mm longer than the Yamaha bolt and with counter sunk head).
This means leaving a few of the Barkbusters collets and expanders unused. This should be fine since the guards will be secured to a welded insert which provides plenty of strength.

First you need to test this set up for correct positioning (as mentioned in previous email) which I think will be fine.

In the worst case scenario, if the guards can�t be fitted to your original bars, you could then still buy the Renthal 7/8� bars which will work perfectly with the BHG15-01 hardware."