Thats a good idea. I agree with the other though, neck down the output. Also, put a screen or some expanded metal mesh over the air intake to avoid sucking debris in there and possibly damaging the blower.
I've see quite a few furnace blowers where the motor mounts on top and drives the blower via a belt, I wonder if they are durable enough to mount a small horizontal shaft gas motor on top. It would be louder but would eliminate the need to drag an extension cord around. Even a small engine should be plenty of power since they are typically driven by 1/3-1/2hp electric motors.