Hmmmmmmm...don't know there bud. I've never seen a setup where the O2's were in a common plenum to both banks before. This is new to me. O2's are standardly mounted at the collector on LT's or before the cats at the collector of each factory exhaust manifold and do not share a common exhaust flow on all four of my FI setups running PD superchargers. It may be different on a turbo setup. Never ran a turbo. As long as wiring is good then you should be good to go. Mike is your tuner so do as he wishes. I already see he is sending you a base tune to get the car in on as well. SO you should be fine. Sounds like its all in the tuning and will be good after you are done. ENJOY!
The 13/14 is my favorite body style. I hope to sell my 17 GT and get back into a 14 GT premium or GT500 before next year.