If you have original 68 heads that do not have the tapped accesory holes in the front, you can either use the bent steel brackets the give you with the headers, or go to an aftermarket bracket that hangs from the water pump bolts.
The header brackets are flimsy. You'll be replacing them every few years, and might have trouble with flexing and belt throwing. They are cheap tho, and mount the alt in the stock location, and don't look "unstock"
The other option is an aftermarket bracket. Allen Groves and possibly March make bracketry for frivers side, no hole head, short water pump systems. These are good stuff, but not too stock looking and kinda pricy.
If you have later model heads that have the holes in the front, I HIGHLY recommend a C3 corvette bracket. These were on all small block vette's from 68 to 82, there are 2 versions, earlier ones are cast iron (paint it orange and you'll never know it's there) later are alluminum.
Here's a pic of my alluminum vette bracket, which I polished.
