We have libraries for tractors and implements with most all of the info you would need. Belt size will depend upon the size of the center spindle as seen below.
44",50" W/4.5" PULLEY IH-59971-C1
3/8 X 78"
44", 50" W/5.0" PULLEY IH-117465-C1
3/8 X 79"
Our belt chart:
http://home.comcast.net/~dos0711/CCBELTCHART.htm
Just out of curiosity, when you are putting the belt on, are you pushing the arm that extends out the front of the tractor that is attached to the right idler pulley, as you sit on the tractor, in and locking it to allow more room to mount the belt. You will also need to back off the nut on the adjuster bolt on the other pulley to allow it more room to move back, then adjust it correctly according to the owner's manual?
You can download the manual for the deck at the link below. It will help step you thru the process of installation and belt adjustment.
http://ccmanuals.info/pdf/QA%2038-44...s%20Manual.pdf