If you simply want to buy a complete kit:
Carls Cycles has a good bolt on.
OR
Rooster Built performance can get you dialed in.
MY MOUNTAIN SETUP> I run at 7000 -10,000 feet
I'm a BIG fan of, first ...Gearing down the sled to approx 2.3:1 and doing this with a 20-tooth top gear (20/46 gearing)...Since you said you have an RMK...easy to do.
I also am a big fan of the Team Rooster weights... allows you to adjust the weight (overall) and the character of the weight in where you place the weight on the arm....62 grams for my altitude/155" track/light-rider.
Stock primary spring (140/330)
TRS has been giving me great advice on clutching and knows his stuff.
As far as a helix... I've been running a custom full-progressive(F) 46-32F ER /46-34F ER with a 120/200 spring (stock is 155/222)
Make sure that your belt side clearance is correct (difficult to change) and that the deflection is correct (easy to change)
I am an advocate of scrubbing the belt with detergent and a stiff bristle brush BEFORE using it the first time and every 3 rides after that...as well as keeping your clutches clean and the faces clean.
Getting a good balance job done on the new clutch is a good idea as the factory can only do so much in a production environment.
The clutches are the 'heart' of your sled...good idea to make sure everything is right with them...invest the time and money to get it dialed, really not that much needed.
.