Just got back from a long weekend and found the good stuff!
I'll take the 57mm outlet, as the rough exhaust calculations point smack into it, followed by the 63 mm final pipe. Its a fully road legal application with 2 large free-flow mufflers; no sense in making undue noise. So it'll be the head pipes going into 2x57mm pipes converging to the 63mm tailpipe. The mufflers will be placed where there's room for them under the car, no experimentation there.
Thanks for the update!

Jim K.