Aquetrac,
I bit the bullet and did the upgrade on my 2150 a few years ago. Bought all the Kubota parts except the alternator which came from Ebay. Expensive but well done by Kubota. It is exactly as you describe with the idler pulley setup. I did post a parts list here as well. The only area to save a few bucks is the air cleaner bracket. They replace the original with a fancy one that has a rubber strap so you can swing the air cleaner assy up to check or change the filter. The old one would have to be un-bolted but would still work fine....
I don't regret it, I run all the accessories I need now in the winter without worrying about the battery....
Best of Luck,
Marty