Oh-h-h-h......! shorty intake boots... how did I forget THAT one?? Lol! One of the performance shops, (suffering from old-timers, can't remember who) used to offer an "induction tune-up kit" or something like that. It included a set of shorty intake boots, and a 501 RV. Maybe somebody remembers who it was.
Get ahold of WinterBrew for a good clutch set-up. DaveB is right - the right clutching will also wake up your sled and make you THINK you added a bunch of power. Big thing is to not over-rev a stock 670. Power drops like a rock and belt heat becomes an issue. If my foggy memory serves me correctly, I think that your target rpm is right around 7900/8000 rpm. Years ago Big John gave me a clutch set-up that worked miracles with my 98x. I was destroying belts left and right until he set me straight. Sled is still kicking butt and taking names ten years later! Got that info somewhere around here...
Clickers - The three bolts around the perimeter of your primary clutch. (actually on the governor cup) They really do not "click", but are an adjustable eccentric bolt that changes the angle of your TRA ramps therefore changing rpm. You have a ten mm nut, attached to the end of a bolt whose head is sunk into the casting. Loosen the nut, and you can push the bolt head out of the casting enough to turn it. The bolt head has a line on it, the casting having corrosponding #'s going from 1 to 6. You can spin the bolt one way or the other, increasing or decreasing your top rpm. #1 being the lowest, #6 being the highest. Each # is approximately 200 rpm gain or loss, depending if you go up or down. Say you are on clicker #3, and running 8100 rpm. Well, you are OVER your target rpm. re-adjust your clickers to #2, which in theory, should bring you down 200 rpm to 7900, which is your target on a stock 670. Handy to use to change clutching depending on conditions - warm or cold air temps, dry powder or wet heavy snow, etc. There are aftermarket spring-loaded clickers available that do not require the use of tools. Ask WinterBrew about them if interested.
If somebody needs a stock airbox, un-cut, I have a couple laying around, along with some various RV discs, and some Aaen twins. I also have an old Don Emory can (vary similar to MBRP) that is pretty hammered, but still salvagable. Had it on my '98x. Hm-mm-m-m.... thinking about all the 670 stuff I have laying around... PM me with a wish list, never know what I might have. Cases, cylinders, etc... time to clean out the shop.