Thanks very much guys for the input. My factory exhaust is 2 1/4 except from the muffler back which is 2". Why Oldsmobile conceived this idea is beyond me. As far as back pressure is concerned, I was always hesitant to that aspect. I believe that my 307 runs off negative back pressure as adjoined with the PCV valve (- Negative). I believed that creating more positive back pressure (in adding duals) would hinder performance. This could be untrue for I added duel exhaust on a 74' Olds Cutlass Supreme (Welded Y pipe) and never had any issues. The gas increased though.
Upon installation this day, the "cut-off bracket" attached to an upper bracket 'perfect fit'. However, the exhaust port opening was leaking some and a gasket and spring needed to be replaced. All is copasetic : finished. I'm not interested in upgrading the 307, too many roadblocks. I'm the original owner and have kept the car all original. If I did decide to go ground up restoration, I would most likely opt for a bigger bullet.
* In terms of flow in the 442 being underrated, I would certainly agree. My 307 has air injector tubes which I replaced some years back. The end point goes into the cat to allegedly lower emissions but if one cuts that tube, more horsepower is gained. The only detriment is a 'hissing' noise. Did not care for the air noise so the tube was re-welded. In the end, what does any of this mean, nothing, absolutely nothing. Again thanks very much guys for the assistance.
I do not recall if I ever posted my video but these are my wheels.