I thought this might interest some of you. Thinking outside the box as usual, I built a custom 1.625" x 32" long equal length 4>1 header which is routed completely above the inner fender, rather than along side the block. This enabled me to NOT have to modify the floorpan to fit the merge collector over the sway bar (a common issue with model 50 Opels). BTW, the merge collector is 6" long, tapering to 2.125", and then another 6" tapering back up to 2.5". I used a v-band clamp so I don't have to deal with nuts/bolts/gaskets.
I also have fitted 3 mufflers to the car in keeping with the stealth mode. So even though the exhaust is 2.5" front to rear, the car will be quiet. This was made easier by the fact that the car is a 1975 California-spec car, so it has a floorpan recession at the passenger seat area for a catalytic converter. I used this area for the first 14" long Magnaflow muffler.
It is all fitted to the 2.5 litre roller cam prototype engine, and is getting ready to accept the cut-down 3.0 litre 6-cylinder EFI intake (cut down to 4 cylinders) and programmable EFI. Should be fun...
Bob