Originally Posted by TrojanHorse

If you're replacing the shifters, I would replace both DRs, the cranks & the cassette (as well as the hub). You can probably get along just fine with your triple shifter on a double crank - just set the limiter screw so you don't shift into a gear that isn't there and use the lower two positions so you don't end up with a bunch of loose shifter cable if you do inadvertently shift.

The crank itself is probably fine as is, but your chain-rings will need to be appropriately spaced for the new drive train and that might be hard. I had a franken crank for a while with an old mavic crank and new SRAM 10 spd chain-rings and I could just never get it shifting perfectly up front. YMMV. If you have a standard threaded BB then it's probably worth just replacing the BB and crank anyway.

I just stuffed a 130mm wheel hub in my 126mm spaced steel frame when I did it back in 1998 and I had no problems at all. I mean really, you're looking at 2mm per side, barely noticeable. However... you should get the frame cold set so that each chain stay is stretched the same amount and stays there. You don't want a rear wheel that tracks funny for the rest of your life.