trouble with 3" is that you have to go under the trans mount on one side (unless you section it) and there is limited room between the tank and the leafs. 2.5 will be plenty even with a big block. So 3" less ground clearance kinda sucks. Id really consider a boom tube out the side, they are duals that come out short of the rear wheel at a 45. They bypass the whole axle and the T/A had similar exits so I dont think they would be a fume issue even with a 'vert. Its just a small frame for such large pipes with no real benefit with your current or future motor unless your going 426/440/451.