Thanks for all of the replies, everyone!
I'm pretty certain that the pulley on the transmission is the original but I'm not so sure about the one on the engine. The original motor has been replaced with a 3 hp Briggs so that might be the problem.
The tractor is currently at my dad's farm so I wasn't able to get any pics today. I'm hoping to make it out there this week to do a little bit of work on the old girl.
If so I will snap some pics and post them up. According to the model number, (9175756) it is a 1950 model year. I'm pretty sure that aluminum pulleys would have been a rarity in 1950 and if I remember correctly there is an aluminum sheave on the motor.
I did have the engine full throttle when I took it for a drive so slowing it down slightly might help.
I'm hoping that by the weekend I will either have a hitch bar fabricated or bought and the plow adjusted so I can see what this thing is capable of. I also plan on tearing down one of the disc gangs and shimming it up to it's at it's proper tightness and angle.
I grew up on a farm and have spent many hours working on equipment but for the last 30 or so years I've been riding a desk and crunching numbers. I'm sure I'll have fun working on the tractor and implements but I'm not so sure that my 50 year old body will be thankful.
Thanks again everyone.