4inch straight through, not a chance in hell.
As for the stock ECU, if you can find 1, plug it in yourself and drive away...the car will be back to stock power and feel like shit obviously, but it'll be fine...no need to 'retune' it as its stock and there's nothing to tune.
Once you plug the pfc back in, as long as the mods it was tuned with are back on the car it'll run like it used to.