I bought some brackets from LS Brackets and they worked ok but I wasn't completely satisfied. If you didn't want to do any big work I would look into them.
Last week I decided to just make some myself. I wanted the Alternator low on the pass side, didn't want anything sticking too far up an wanted to maximize belt wrap. This is what I came up with. It's mainly going to be 3/8 Alum plate with some spacers and a small mount for the alternator to the side of the block. It isn't too hard to do. This is a prototype using MDF. I'll try to get it cut from Aluminum later this week.