Give it a try and let us know if it works. Most of the indexing will distances will be determined by the shifters, when you change the Command levers to index mode. And you're using the XC-Pro hub with the correct cassette, so you're almost home. I'm thinking there's a strong possibility that the rear derailleur "pull" on a pre-index SunTour is likely the same as a later indexing model. And like you said, you have the fine cable adjust that you'll need on the downtube, so technically, the RD won't need one. Even if it doesn't work well you will have just set up all the elements to the real deal, you can just continue to run it in friction mode while you source a SunTour indexing RD that will be better. The supply of XC-Pro RD's seems scarce and ebay-ers can get pretty competetive going after these driving prices on new ones over $100 at times, but they made different flavors of Accushift compatible rear derailleurs, Yellow Jersey has a stash of nice, NOS SunTour "X-1" long-cage, black anodized rear derailleurs for $49 each. I have one on my Puch running in 7 speed index mode and it runs like a champ. I imagine that if you start looking that there may be any number of XC-pro, XC-9000, XC-7000, XC-Expert, XCE, variants out there that would be suitable. Hardly anyone is using this stuff anymore, which you could use to your advantage I suppose.