I did the same thing, had a machinist make the hole bigger, he fucked it up and got it off center ruining the housing.
I'm sure you noticed that the roll pin holding the gears in the housing is "blind" in that it only has ONE hole to push it in with no way to push it back out from the other side.
Since I had nothing to lose with the ruined housing I ended up drilling a tiny hole opposite of the "blind" roll pin on and removed the roll pin and gears and installed the new gears in my old housing...After figuring out where and how deep to drill the new hole on the old housing I had a "method" to use to remove the roll pin on my good housing to allow removal of the old gears.........Works perfectly now......With a 120/70-18 it's about 1.5% off....
Boxxenstopp shows/showed a correct one on thier website for about $50, I was trying to outsmart myself and orderded what I thought was the correct one from the dealer for about the same price....I was wrong...
Huh, didn't think about swapping the gears over...figured couldn't be done. Yeah, rip-off from Boxenstopp. Now that I know that I need a YZF600 drive I'm set...just need to shave some meat from it so that it fits the fork on the left side.