Lord C.
You have gotten as definitive an answer as you can get on the 1st, but let me share my experience.
Most rear hubs have about 8-15 mm worth of spacers on the non drive side. Of course they are there for a reason-to keep the chainline right etc. However, if you aren't a mechanical perfectionist-(many members here are ,to their credit)-you can remove the spacer and replace it with some washers(take out 10mm replace with 6mm) etc, so you don't have to stretch the rear triangle.If it doesn't have a removeable spacer-and you don't care about using the wheel anywhere else-you can grind what spacer is there.
If you really really aren't a mechanical perfectionist you can fit 135 hubs on 126mm rear spacings.The wheel/cassette will be offset to the left 4mm, and the tire will be 4mm closer to the chainstays-there usually is enough room to accomodate this. The bikes still track true with hands off the bars-not sure why.
The above is strictly jury rigging to the max.I did this to put 26" MTB wheels/tires on a 1978 road frame. I use (95mm long reach) BMX brakes to reach the rims-a trick I picked up on Sheldon Browns site.The other abominations-cockeyed wheels- are strictly mine.
Luck,
Charlie