You probably only need a cylinder kit for the 660. The cylinder is just aluminum, whereas the lower end is almost automotive strength. I've had good luck with the aftermarket kits off ebay. They're pretty easy to change. You can take the oppourtunity to go with a big bore kit, but that's a few more dollars, and the saw has plenty of power pulling a 42" bar with .404-.063 chain anyway for me.
You don't really need any special tools, other than the T27 T wrench that fits almost everything else. You don't need ring compressors or any of that sort of thing. Fingers work just fine. Notice that there's a little pin in the ring slots. The gap in the ring has tapered ends. I don't remember which way they go, but look at whether the little pin is at the top or bottom of the slot, and put the ring on accordingly. I broke the first ring I put on by putting it on the wrong way, and trying to put the cylinder down over the piston. Oil the piston up good before you slide the cylinder down over it.
The good thing about the Stihl T27 wrench is that you can feel the shank twist when you have reached the proper torque. The manuals call for all sorts of different Locktite for each location, but I've always just used anti-seize, and never had anything back out, and no problems taking anything back apart with galled threads.
I have a Poulan that doesn't run that I give to anyone who wants to borrow a chainsaw. I'd never loan out the ported 066, 036, or any of the orange saws.
