Tim - if it has decent compression, grab it. I have no doubts you can find a good home for it here somewhere if you don't keep it. I am down to 2 PM800's right now, could always use an extra few around. I would even pay a bonus for one with the coarse thread compression release above the muffler and no Q port...
Cobey - the OEM carburetor for the CP 70 is rather unique with larger throttle bore than other SDC's, like the PM800 with the compression release, I would pay a bonus to have a few extra SDC18, 19, 20, or 22 carburetors.
I did notice another McCulloch carburetor guide in the latest bunch of literature I picked up that seems to have some additional carburetor not listed in the SI-29 book.
If I ever get to spend some time at home and/or in the office I will try to get the later guide scanned and make it available.
Mark