I cut the aperture linkage lever to flush with the rear element retainer ring, and as you can see the rear element is full, it has no cut like M42 version.
The diameter of this rear lens is 34.5mm +/-0.05mm, whereas ML 55mm's is 35.5mm +/-0.05mm. According to the information from one of my friends
PORST COLOR REFLEX 55/1.2 has three different models, the first one has Fstop upto 16, this one has 22 so this is later version thou I don't know which.