The system starts with a manifold and downpipe from a 4000 Quattro.
They have not been drawn.
First is a short flexible piece to help reduce strain from engine motion on the manifold studs.
Then this curved pipe, which provides the appropriate straightening and offset.
This is also where the OXS bung is welded in (not shown).
The catalytic converter is in approximately the stock location.
The 2.5" inlet/outlet unit I used barely fits, but does not rub.
The section after the catalyst runs straight and clean down the center of the tunnel.
Clearing the narrow part near the hand brake cable boot takes a little care.
Just after the tunnel I installed a pair of flanges to ease future disassembly.
These curves left no room for a resonator. Oh well.
This curved section over the axle and panhard rod was built from just over two and a half ninety degree bends.
Luckily the radius of the mandrel bent pieces was appropriate for this job!
The muffler I have settled on is a DynoMax Super Turbo, with a center 2.5" inlet and offset 2.5" outlet.
I made a piece of 1" x 1/8" galvanised steel into a wrap around strap, and to that I attached two brackets out of 1/4" rod. It hangs nicely with the stock two donut system.
This leaves the muffler outlet low and inside of the bumper cutout. Two 90 degree curved pieces gave up their lives to get the pipe over to where it belongs and make a dual outlet tip.