I've done the same upgrade, up to 200a with a 1.9 inch pulley. It is very easy to install, and can be done really cheap. I wasn't sure about that adapter from alternatorparts.com for 2 reasons. One, I have the Gen V so I don't know exactly where it would place the alternator on the bracket. I already had to do some grinding to fit it, and I have about 1 or 2mm between the supercharger and the alternator as it is. Two, I was screwed over by the owner. He was very helpful wish diagnosing problems and giving me troubleshooting instructions...until his rectifier was the result of his own troubleshooting. He stopped answering my calls, and said he doesn't warranty any parts unless he installs them. From there I sourced a new rectifier from ebay, for cheaper, and look identical to the alternatorparts' rectifier.
On top of that, like you mentioned the adapter is damn near the same price as a new tensioner. I have a little mini write-up on the 200a upgrade in my build thread, let me go find it and post it in here...
