Jamesw is correct, in that they are O269 and O271.
However, for the specialized perfin collector, there are two types of 4-hole perforations for this issue. They are identified as 'O8' and 'O9' in the catalogue "Canadian Stamps with Perforated Initials" by J.C. Johnson /G. Tomasson.
The diffence is mainly in the shape of the 'O', during 1935-1946 they perforated with a narrow 'O' and during 1942-1949 they perfoarted with a wide 'O'.
You will have to get some more to compare!!
The prices for the different versions and also the rotation at which the 'OHMS' is perforated on the stamp can change their price drastically.
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