It's just an 1-1/4" keyed shaft from Surplus Center.
1-1/4" X 72" KEYED SHAFTING 1/4" WIDE KEYWAY
Not sure what your question is about the double chain setup?
Thanks! Instead of a single drive chain run a double chain/sprocket setup to prevent the chain from snapping.
Note the sprocket: http://www.tractorbynet.com/forums/...1d1256566206-shes-done-power-rake-build-8-jpg