Here's an idea for ya. You need information about both sleds before you do anything.
Get the hp power curve and weight from both sleds first. Then do the math. Try to match the Yami's weight and hp to the f7. I think the f7 is about 140hp. Easy enough to reach, but the weight is going to get a bit pricy. As said above, lightweight skid, front, etc. will get you in the right direction. I would work on the low end seeing how thr f7 is a twin and the viper is a triple. Once you hit your mid, you'll most likely leave him behind. I don't know, Just some thoughts though. I did alot of this stuff to my 00 SX700r plus a few engine mods and I have beat most twins out of the hole. I have never matched up against a f7, though.
I actually did alot of this for the same reason. I couldn't beat my buddies Polaris 700 twin. So I modded until I did. You know what? He still beat me because his sled is stock. I may be faster and quicker, but I have a small fortune invested in a sled that I will never get my money back from and he has a stock sled with better gas milage, etc. He still gives me crap" Yeah, you beat me, but I didn't have to take out a loan to improve my sled"
It was great, though to whip him that first or second time, but to me it wasn't worth it just beat a sled. I enjoy the power of my sled, but you get the point, I'm sure.