My next sled I think is going to be a Ski-Doo. I want a 136'' or 141'' track, so that would leave me with a Summit. Which would be the better engine for a mid-late 90's Summit...the 583 or 670? I've heard good things about both but some further info would be great. I've ridden a 98 Formula 500 (s chassis) for quite a few miles and I liked it a lot. I've seen the mainly around $1500 or so. I would probably need to do a few buy/fix/sell cycles before I had enough to get one, but I plan on finding another job and saving as much as possible. Please give me the lowdown on both the 583 and 670. R.A.V.E. a recommended choice or stay away? Thanks.