6401 with a @fordf150 7910 top end. Zero fitment issues besides drilling a new hole for the decomp which you can just barely see behind the top handle. No big deal, less than a minute with a cordless drill and spade bit. Have the new top covers, but they are saved for a side project. My friend makes custom carbon fiber car parts and is going to teach me how to mold and make the top plastics in carbon fiber. So I'm keeping them fresh and clean till the time comes. Then they still won't be used. Had the top end for about two years before finally getting around to installing it. The saw ran so good as it was it was hard to get motivated to tear into it. Haven't done anything to the muffler yet. If the new ones don't melt with a cat in it, the old one isn't going to melt because the opening is a little smaller than that of the cylinder. I'll get to it one of these days though. Whoever said the factory kit isn't made for the saw has been fooled.... it is the same crankcase/crank with different stickers and muffler configurations. One could get the 7910 muffler, but you would be doing yourself a disservice. Just like getting any of the aftermarket top ends. I'd rather have the original 64xx and still have a great saw with plenty torque and better fuel efficiency.
