This is literally exactly what I want to do, except with a t56 magnum and a more built LS3. I was thinking more dual 3" exhaust but I'm not sure it'll fit. I really dont want a single 3" though. I have a couple questions though.
Just thinking here: Since you use different front differential mounts now, could you cut the middle piece of the old diff mount that has the exhaust bump (that causes pipe fitment issues) and leave the brackets holding the LCA? Also, have you looked into getting aftermarket drop-mounts/dogbone? The stamped sheet metal holding the other end of the LCA scares me, but I'm not sure what aftermarket ones could fit behind the ford diff cover you know?