I am assuming that the sled had spark before the engine tear down and the parts going back in are the same parts that came off the running engine and that you have triple checked all the connections.

First I would unplug the wireing harness from the sled and check to see if there is spark.  The engine should run without being connected to the sled harness.

If it sparks then, the problem is on the sled side.  I would check the kill switch first and then the key switch.

if no spark then it is in one of three parts on the engine.  Spark coil, CDI and flywheel.  The last time I had no spark on a rebuild i found the flywheel key had slipped out on re-assembly and the flywheel was not timed correctly.  While I have heard of CDI's going bad, I personally in several dozen sleds have not had a bad CDI.
Okay thanks. I'll be looking into this tomorrow, and I'll let you know.
Let us know how it goes.

I'm hoping for some open trails this year.  My sleds really need some exercise.