Since I wasnt satisfied at all with a recently fitted Regina Chain (there was 0,4mm play between clip and plate), I decided to try the RK chains.
The RK 530 KS is 20,75mm wide and fitted without any problems or any signs (suspicious noises) of contact to the case. The KS is already an improvement, evidently stronger than the Regina and I installed it with a rivet, not a clip.
I also tried the 22,6mm wide, sealed RK 530 uwv, which unfortunately did not fit, but got stuck.
As I am planning to install an new quadrant and G46 this winter, I will check again and try to find out, if it is safe to remove some material to get the necessary clearance for the 530 uwv.
It is a 1951 Rapide Engine.