As far as the double blades,
#1,
I wouldn't recommend any welding as it is unsafe and a balance issue.
#2
I tried stacking one blade on top of the other to resemble a centered cross, as a trial once.
It took more power to operate, didn't improve the cut one bit and did not discharge smaller clippings or throw farther, but it did make a louder "roaring" sound while operating.
This was on a 50" deck with 18 hp.
Your results may vary, no animals or endangered spotted zeta skeeters were harmed, or earthworms disturbed.
