I'm making plans to build my own controller for my NES using a SNES controller for the base.  I'm planning on leaving the D-Pad intact and ignoring the shoulder buttons.  I want to wire in the X and Y buttons to act as A and B and want to try to wire in the A and B buttons to work as turbo.  My plan is to scrap a NES Max or other turbo controller for parts. 

Any suggestions before I begin?

Here's my sources that I've been using.
http://www.neshq.com/hardmods/snes_to_nes_controller.txt
http://www.slagcoin.com/joystick/pcb_diagrams/snes_diagram2.jpg
http://farm1.static.flickr.com/41/83558315_02c1a79a0d.jpg

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I'm not sure how I would like that setup.  I have never been much for turbo, although sometimes i end up using my thumb to press down two buttons at once.  This might make that easier.