Does installing the 727 mod cause problems with the tansmission on a '03 Raptor. Is there anything else you would have to do to the bike if I did the 727?

Is this the best one to get?

 

You could always have the gears cryo treated if you are worried about them giving you problems. And yes..there is a LOT you have to do to the bike to become a 727(the right way)...and it's expensive. Most would be happy with a 686..and it seems like that might be a better choice for you if you are worried about breaking things. Just my opinion.