Can you post a picture of the front axle? From what I see, that IS a 2135. (OR...UK 135, also sold in Canada) It doesn't have the swept back axle and radius arms of a US market 135. As Robert said, the PTO SHOULD be under that screw-in cap on the rear end of the differential housing. It's possible that the pto stub shaft might have been removed, but from all indications, even if it IS gone, you have the same rear end as a standard 135. So....If the stub is gone, it should be feasable to replace it. Also, there is a pto control lever on the left side of the transmission housing, approx next to where your left heel would sit on the running board. (visable in photo #1) That wouldn't be there if it was not originally equipped with a pto shaft.
I've seen a BUNCH of 2135's (also MF20 Industrials) that were repainted in the red/silver AG tractor colors. If so, whoever did so swapped out hood emblems and used 135 decals. Yours has been repainted at one point. The grey chassis color is older "Ferguson" grey and not the flint grey metallic that would have been on an original 135.
I'm digging through some old info to see if that "odd" serial # is one that would be found on a UK model 135. (UK 135's built in the 70's had a straight axle on the front that you wouldn't find on a US market 135)