Im going to point out a couple things and well you guys just run with it. I havent done this so Im speaking from an entirely observational point of view.
1. I believe the brackets from the Bonneville can be used in the Grand Prix with some minor modification. Ron Vogel has done this I know of so he may be better to get info from with regards to that.
I persnally am using an L36 bracket on mine, with a custom engine mount on top. The L36 bracket I changed to put the tensioner in a little different spot than stock. I did it the hard way, so it can be bolted to the stock location, and so the bars are more parallel than just bolting it right to the head. The easiest way to do it, is simply welding a bracket to the rad support, and bolting the heim to the head with a spacer. It probably saves 5-7#'s on the upper mounts, and 10 or so from changing the tensioner bracket.
Where did you get that red mount that holds the hood latch on? that is cool I bet it brings in a lot more cool air. I want to do this for my 04.
I get too much air to the rad, I have cardboard in front of the rad for winter, and even on 50-60 degree days can't get the motor above 170 in stop and go traffic.