I ran a Sigma alternator for a about 10 years... internally regulated, bolts up to the standard 120y mount on the block. I'm not sure how many amps it put out though or exactly which sigma it was from. It worked fine.

VN Commodore alternators are a pretty common conversion on a lot of modded cars - you need to swap the pulley for a v-belt type one (the Commodores have a serpentine belt). They output 105 amps. Not sure how close they'd be to fitting a 120y though.