The front part has to hold the lens. An adapter from 75/63mm to 63/50mm is used for this. 

The rear end is turned down from 63mm to approx. 59mm. The exact diameter depends on the inner diameter of the 63mm tube. The goal is to push the 63mm tube onto the adapter.

Inside the adapter the flange is turned away to have a free path to the lens. The flange is normally used as a stop for a 50mm tube which is inserted inside.

The front side is turned up to about 67mm. The exact diameter depends on the diameter of the Beroflex lens block. To achieve a certain degree of glare protection the lens block is mounted as far inside as possible.

The lens block is held by three m5 headless pins. For this purpose three holes are drilled at an angle of 120° and provided with M5 threads.

To avoid reflections the inner one has to be blackened. In this case I simply used black spray primer. Not the best solution but a reasonable price.