I got a 140 amp alternator from a company called "National Quick Start" by doing a google search. I don't know anything about the company or if the alternator is any good. I think they just change the guts out on a larger frame Delco alternator. They sent me the appropriate adapter connector/pigtail as shown in the pics. So far, it seems to work OK -about 3 years - I just got it for help with charging dual start batteries. However, you really don't get a big output from these alternators until you crank up the RPMs, and my in town (mostly idling driving) is better than stock but not really max. output.
I just bent up the upper mounting bracket, as I recall, and made this big boy fit. As I recall, I did have some trouble keeping the adjustment slot in line, but I just tweaked a bit at a time and I got it to barely fit. I think persuasion was provided by a big cresent wrench and tire iron.
I think it cost about $160 including shipping and the new adapter.
I also think the shop that did my remote starter upgraded the wire size from the alternator - necessary mod when upgrading the alternator, as I recall reading. A bigger wire to the starter is also a good idea, especially on Big Blocks like mine.