Van Veen Rotary inlet rubber Manifold:

This beautiful piece was originally designed by the Van Veen team for use on the GP Kreidlers.
But its useful for other applications too.
Distance M5 screw holes is 60x26mm.
Inlet hole itself is 29mm.
The carburettor needs to be modified to fit in the rubber ,it will have a very short L-shaped ridge ,aprox 8mm of length.
This ensures the shortest possible mounting.
One big tip for mounting: Put 4x M5 washers under the rubber to prevent it from bending when the screws are tightened hard.
A bent rubber can let air leak in !