You are not the first to put 3" pipes on an A-body !
Wait till you get to fitting the 3" tailpipes out to the bumper, you're gonna have another "can't be done" moment !
But it can, and has been by many.
Find a good muffler shop.
I did get a miracle worker to get 3" over the diff and they come out right behind the back tires to limit back pressure. The header on the pass is too long, trust me. I will try to get a pic up in here in the next few days. I do believe a good exhaust guy can fix this, but I also think the header is way too long, I'm fairly certain he will need to cut about 4" out of the collector. There is just no room to 90 towards the exhaust cut out in the cross member, jog over to it then 90 over towards the back. It can't be two 45's, no way.
