Wheel drive belt for 7HP White's Snowblower

I have a 7HP White's Snow Boss 750 (H633E) , MODEL number 31AH633E190, SERIAL number 1K169B50456 as taken from sticker on machine. 
 
I am trying to find a belt that drives the rear wheels. I am at the end of my rope with this POS. The manual states 754-0343. I can't trust the dimensions of a belt to find a replacement, for example a 3L290 is a 3/8 belt that's 29 inches in length. 
 
I have bought several belts around what I think the size is only to find one belt is to long and barely drives the machine and the other belt is to short to fit on the machine.
 
I don't trust using the dimensions of the old belt because it gives me a length that turns out to be long when I buy a belt based on the dimension.
 
Just what am I missing , this is not rocket science yet I can't find a belt that works.
 
Please help me!