Ok so after much pestering from my wife I decided to fix my leaky shower head-- I got the new cartridge and stem from Kohler with new o rings. Pretty simple right-- no! As of right now- when I turned the water back on it is on all the time from the shower I thought maybe I had it upside down-- flipped it around same thing. Swapped the o rings with the old stem and used that-- it worked but leaked from the bottom. Tried to fix that but now I am back to the constant on. Can anyone give me any advice on what to do to fix this. It should have been a simple thing to do. Thanks!

I'm afraid I may have had a dumb attack.I am remodeling my bathroom slowly piece by piece('48 bungalow). I have a standard tub and shower that I took the walls down to the studs and put up Durock and have re-tiled. Not thinking at the time about new hardware fixtures I tiled around the existing valves and spouts....Here I am a month later and I'm ready to replace the fixtures throughout the bathroom so my question is can I just buy a 3 handle shower set or do I have to worry about the handles ,etc..fitting the valves? Thanks.