Hi Arne,
It would have been great to build a Corrado with a TDI engine, but I ended up getting a Golf III TDI GTI instead.
Regarding your problem:
The best option that comes to mind are the silicone hoses from 'SAMCO sport' (available at SANDTLER).
They are available as straight pieces, as well as 45°, 90°, and 135° elbows, and as reducers for almost any diameter (certainly for 60mm).
Advantage: The hoses are pressure-resistant, offer flexible adaptation, and are suitable for temperatures ranging from -50 to 200°C.
Have fun with the renovation.
I would like to see the results of your work sometime.
Regards,
Michael.