Additional information to what Scott has been posting, I have 2 149"s (1) SN 442961 mfg. Aug 72 purchased summer of 78, (2) SN 490127 mfg. Nov 73.
Here is a picture of the Aug 72 - 149: No holes
Just for reference in the same post, here is my 1450 with the holes: You can see them in front of the brake pedal
I don't have a picture of the Nov 73 - 149 and with it being winter I'm not sure Dad could get to it... but I would guess it has the 3 holes because it had a brake type PTO.... The pictured 149 does have the PTO Safety Switch.... so it is "new enough" for that update, but old enough to not have the holes.
That one was our work horse for years.... it was the only one we owned (we still have it, it just has a bunch of company now), so it did everything. 5Snow, Mow, Till, Plow.... you name it... it's semi-retired now as it get to wear the blade and chains year-around. It has probably 2500+ Hours on everything but the engine... and it's on the 3rd rebuild of the 2nd engine (1400+ hours on the engine, except the rod, piston and gaskets to get to them).... which is why it's black. You can see it's younger brother in the background.... that one has taken over mowing duty......