if i can get my hands on an ignition advancer for my gs how much should i pay and is it worth it?
Second  If i were to swap front ends what year katana and what year gsxr would work.  Please include engine size.

are you referring to the one on ebay for $10 or so with $10 shipping? If so.. just mail your stock advancer to bob broussard and have him modify it, same as a K&N, but he does it for $5 plus shipping the sprocket to him and back to you.

lol, front end swap, any will work any size ....... but.......
you have to get the top and bottom triple clamps and press out the old stem and press in your gs stem.
there is a write up in the wiki.