When you do the brake boss bolt up as tight as possible, can the cantis still move about freely? If not you need to clean the brake boss. I found that to be a real problem with curves. Gets some sandpaper/wire wool on it and then greese them up.
The next bit is quite fidly. you have to use a spanner on the red (usually but sometimes black) spring tension bolt and crank it arouns so that it statrs to pull the anti outwards, then do up the brake boss bolt while holding the spring tension bolt in place.
I don't know if you ahev tried this yet, sorry.
I have a pair of fairly worn Scratch and Sniff tyres and a pair of NOS Enter / Break tyres. I have a Mavic 238(?) on a Kona SUS front hub, off my very first, a Lava Dome.
Let me know if you are interested.