Actually, the 42" blades are all the same, it's the sub-frames that are different, I believe there are at least 3 different ones for the Narrow Frame tractors and yet another for the Wide Frames.
In the illustration I believe the one from your 147 is #22 and you need a #15, I don't remember if you need the extension arms (#19) or not.
http://www.partstree.com/parts/?lc=c...&dn=0068200001
Someone please correct me if I'm wrong but, I keep thinking that the Narrow Frame Quick Attach sub-frame that you have should bolt up to your 71, the "pins" would end up being just below the tractor frame, but it's late and I just don't remember.