Just to clarify your post in simpler terms, a 'custom' tune is not required. Just turning off the rear O2 sensors is all that is necessary.
I have NEVER put long tubes on any of my cars and not custom tuned each vehicle. Each car is different and I would NEVER trust a canned tune without checking AFR on the dyno and if you need help you can call my tuner and pick his brain.
Bruce Tucker = Tuned hundreds of Ford's via SCT.