If the B7500 that you have is a newer B serires, it will fit but the subframe kit that holds the blower to the tractor might not. The older B tractors, B7300, B1700, B2100 & B2400 used a different sub-frame. The newer B tractors use a different sub-frame which is significantly different. I'd bet the mounting holes on the tractor frame are different too. I suspect the new sub-frame might need some creative thinking and modification. It shouldn't be a complete nightmare though.
The unit you mention runs for about $2900 with tax in SE Michigan. If the price you're looking at is half, then it might be worth it to buy it from your source and modify it to fit.