I'm assuming the bike ran before the top end work? Start with the basics and work upward from there...1) make sure you have spark and 2) make sure you have fuel.
If you all of a sudden don't have spark since the bike was apart - I'd assume that a bike of that age - you may possibly have broken a wire during assembly/re-assembly. The place to start there is to unhook the kill switch - which, when operating properly, is a known short on purpose. Then check ignition/CDI connections and grounds. (Was the flywheel or stator off during the work? Is ignition timing wrong?)
If you have spark, then check your plug to make sure it's wet. If it is - then move on. If not - then try to figure out why. If it's wet and you've kicked a bunch of times - try a new plug and work on your starting technique...1) if choke is on, leave the throttle closed. If still no pop, then close the choke and kick while holding the throttle wide open a few times.
Your bike is pretty simple. Take your time, start with the basics, and move up the ladder from there.