Yes I triple checked piston direction. Also made sure the piston rings were facing the correct way so they wouldn't catch on the holes in the head. (Edit - now that I think of it, I couldn't move the rings, they only had one way to go in around the protrusion on the ring fittings. But I did make sure it wouldn't catch on the cylinders)
I cleaned the old reeds extremely well before reinstalling. Made sure all the flaps were in good shape. That seems to be okay, but I don't know what a defective reed looks like.
Compression is the only thing I didn't check yet. Will do that tomorrow. I just thought I read somewhere it's pointless until after everything is broken in.
I can't think of anything I did differently during the rebuild to hinder it from starting. Front flywheel was lined up according to the markings I made, as well as the marks it left by the holes when removed. This was also aligned differently than the manual had, but I made a post about that here and confirmed they had two different alignments on the 951s.
The carbs had been sitting, even after I rebuilt them. Didn't plan on it, but my day-to-day kept me from getting back to the ski. So let's just say a needle is stuck somewhere, would it keep this thing from starting even after putting some fuel in the jugs? Even if only firing for a second or two?
Was also mentioned to me that oil can sit in the crankcase and cause issues? Is this a possibility after having sat for a while?
Cylinders seem quite dry. Turned her over without plugs in and nothing. When I pulled the plugs today, from after trying to start yesterday, like I said PTO had a drip of oil on it, and the MAG plug was clean. I'm wondering if clean is a bad thing in this case.