This morning I was able to finish the circuit:
Some initial tests showed the circuit works. Below you see the generator supplying a nice sawtooth:
Measured upper frequency is appr. 265 kHz. Final steps are the +/- 12Vdc power supply and the casing.
Since I had the oscilloscope, a Handykit HKS130, in front of me, I took the opportunity to apply some contactspray into the potmeters. After all those years they needed this. This type of kits were popular in the 1975-1985 era. It was fun to glance at the contents of the kit and to see how the scope had been designed:
Contents oscilloscope Handykit HKS130