I was with sawdust on the muffler, but some of those are interchangeable. The cylinder flange is the same, a lot of times they just changes the shape of the deflector. I had the same issue with the choke lever on my 770 until I realized that the Tillotson carb was not OEM. It was originally shipped out of the factory with a Carter carb. The choke on/off works in the opposite direction ofthe Tillotson. My giveaway was that the H/L screws could not be adjusted thru the side. Some of the older production saws had the Carter, then tillotson was installed in the later ones. I have no idea what the ratio is(carter to Tilly), or when, during production, the switch was made. It's either a Bantum or a 660. Glad it's a runner. Your pics of the blue Mystery Monster are a lot better than the ones in the listing.