Your other problem might well be RPM's.
A rear blower generally is designed to run at 500 RPMs and front blowers are often driven at higher RPM's. as many are driven from the engine crankshaft, particularly on garden tractor style machines.
A simple reverser could be made using 2 gears mounted between sturdy plates, problem is bearings, shafts, U-joints etc would all add up fast to $$. making a factory reverser sound cheap.
Smiley's idea of twisting belts is your best bet even if you need to add a few pulleys to guide the V-belt around obstacles.
And Hi SMILEY from Ste Adele!