A couple of things having halfway scanned the last 2 pages...
Your belt tension is low I think- Where did you get the 50 lb figure? A quick google makes me think it may be about double that... Then remember that you have the tension on both sides of the pulley- so double it again! Also, that force is cantilevered out significantly far out there on the blower nose- it's going to create a moment around the entire part and load up harder on that end cylinder... I can't really tell where you are applying the load, but it may be something you want to check.
Also, have you considered the dynamic loading created by blower drive torque? Vibration will be a major issue as well I think with that heavy of a mass hanging out there... I would check the natural frequency as well- it may be low with that big old mass out there and a sufficiently soft / springy system.
Food for thoughts.
