[jdkskyking]

You will find that if you carefully cut the mounting flange off the old unit that it will be easy to weld onto the new one. You could make a new flange out of flat bar and simply transfer the hole locations.

And if you dont have access to a MIG unit, you could make a mounting frame out of angle stock and bolt it tonthe fan.

The old blower and the new blower are exactly the same opening size

Sounds easy enough thank you. Yesterday I was working on the fan and motor, one of the rubber foots had come off the adjustment screw which would allow the unit to vibrate. Mike told me about the modification, that will make a big difference. 
JK