How much extra chain you have?? Check and see if your rear wheel is more forward or rear on the swingarm. If its farther back then you will prolly have room. But actually I would think you'd be better off fitting a 15 front and 50 rear versus just a 50 rear since you'll gain some slack for the rear from lowering the front. Just remember about chain size, gotta get the right size sprockets. Also I heard its a good idea to change sprockets and chains at the same time as they wear about equally. I would spend the $130 and get the sprockets and 520 chain combo off ebay. I got it and love it.
I wasn't for sure as to whether or not i wanted tto doa full sprocket ad chain change.....but thats what i'll probably wind up doing i've yet to hear anything bad about so i might as well.....Thanks guys