There's a difference between the Comet/cat 6 post clutch and the AC 6-post clutch from the 07. The 07 is a lot stronger, and is a 33mm clutch. The 9-post and the older Comet/Cat 6-post are 30mm. I would look for another 9 post, the older Comet/Cat clutches are really weak and require frequent rebuilding. The ring gear won't matter, some guys run them on starter-less engines to add some harmonic dampening to the clutch.
Knowing how inventive Cat guys are, I would not be surprised if there is an adapter you can get that converts the 33mm clutch to a 30mm crankshaft. Maybe KCCats or RJGleason can weigh in...