Great step today for getting the car back on the road (with flat six still). The right catalytic converter showed up yesterday. Today I was able to transfer the o2 sensor, some plug bolt and block off the second O2 port. Then the pipe was mounted and after a bit of wiggling all fits now
Also hang the rear bumper cover to check clearance, positioning, angle.. The muffler clears my gearbox (which was the whole intention behind getting this sausage type muffler as the stock muffler doesn't clear the G87 gearbox) and also enough space to the bumper cover. At the moment it sits a bit off-center, but I hope I can wiggle it some more to get it right.
Next step is to make a bracket to hold the muffler to the gearbox. Part one of carboard template is done, part two to follow any time soon. Then I'll make a metal version. That should allow me to mount everything back up.