Yep nailed it. I've spent about 8 hours over the last few days reading everything I can find lol. The 4 bolt Colorado/Canyon AR5 guarantees you'll get a bottom mount, on the 6 bolt solstice afaik only the 2006 had the bottom mount.
Another thing to think about when choosing which AR5 to go with, is shifter location, the 6 bolt solstice/sky trans places the shifter about 6 inches further back then the colorado/canyon version. As he posted in this thread, you can use the jzx shifter assembly (33570-22150 , 33530-22300 ), although the parts are about $450 today.