If I remember correctly, the largest AC Delco alt for passenger automobiles is 135amp. And that's for an F-350. I could be wrong though.
More then likely he lied to you to get you to pay more.
I have a 240 amp davilco alt on my bagged truck, and with both compressors going, SAZ-2000 at .5, SAX-100.4, and the HID's on I barely dropped to 13.3.