There are countless ways to do it and having a price range will help us know what mods to suggest.
If you are mister money bags go full billet mattoon cases, chariot billet stator cover with bearing support, straight cut gears with a billet basket possibly with the option to run 8-10 plates and or a lock up, a lock up cover, etc... There's more I just can't think of off the top of my head as I would never build this type of motor for my type of riding.
Do some research if you're serious about this, talk to one of the site sponsor builders. Right now most on here would feel as though they're wasting their time giving suggestions to a kid with big dreams, at your age you should be trying to learn all you can, read and search all over this site and soak it all up.
At 15 I don't see how you are affording several thousand worth of mods on your banshee in the engine alone, like mentioned before, you should be spending money on your suspension FIRST as with 55-60 hp you already have far overpowered your set up. If you want the big motor you should be dropping another 2-3 grand easy on your suspension FIRST.
I know you want the best of the best and the most power possible, I understand the mentality. However, you need to step back and analyze what is practical and what you will be doing with the bike and mod accordingly to accomplish this without any overkill and spending 10 grand on a trail bike.