ultranator bracket replacement

I'm going to suggest possibley taking the old off first, and then putting the new on, but i might have gotten that backwards.

It depends what bracket you're looking to change. there are two. A bracket at the bottom that holds the alternator in place and an adjustment bracket on top to adjust the tension on the belt.

The adjuster bracket, looks like bolts wont come out past pullys.I'm guessing the pullys will have to be removed. Is this right?

Just turn the pulley till one of the spokes are open over the bolt. That way you can remove the bolt with a socket wrench.