I don't understand why you would even try to put a 135 spaced hub on a 126 frame. If you are going to mess around with this at least start with a 130 hub. And there is a reason they went with 130 spacing and that is there is not enough room with 126 to get 8/9/10 speeds without sacrificing strength somewhere else. And as Alcjphil says, 126 is not the current standard if you are looking to get it to current standards. Don't do it, you will find that it doesn't work smoothly, that there will always be one gear or another that won't shift or rubs. It just seems crazy you are going to build a wheel that doesn't meet the specs and go through all of that trouble to make it work when you could build something from scratch that does.
I know the itch to be creative with making things work, but at some point I usually throw in the towel and buy the right part. And there's the key, if you are going to buy, buy the right part from the beginning.