As said, I would need to custom make the part between the exhaust manifolds and the Simons silencer. Another friend and college accepted the challenge to build these custom pipes:

The tricky part was to get the exhaust pipes right for the moving steering bar, that comes up a bit when steering. So one of the tubes needed to go upwards a bit before going downwards.

Oh, and I got a new clutch slave cylinder! The Valeo clutch set works brilliantly! 😀

Some midnight testing of the exhaust: