Hey, that looks familiar! I just finished doing the same thing to my 1980 Excel V. However it looks as if you've got some more work to do on the wiring harness than what I did. Pay immense attention to the ground wires, as you can't make them too good. Good grounds will go a long way to making it reliable.
Also, check out the end links on the steering linkage. I found that mine were loose from vibration, and when I tightened them up it make a huge difference in the handling. Now's the time to do it while the engine is out.
I also found that a commercial degreaser and a black bristle brush is a great way to clear out the black sludge that was stuck to the bottom of the floorpan. Used liberally, scrub it out good, then hose it out. Then do it again with Engine brite! Mine had half an inch of grime and old seed pods that were left by the rat/squirrel/mouse which nearly totalled the sled.
Lastly, I also took the time to remove the seat, tank, and airbox in order to switch out the old fuel lines. I also had to clean the airbox of old foam and seed pods. When I was done, I partially filled the side baffles of the airbox with mothballs. It didn't seem to harm the performance any, and you can occasionally get a whiff of naptha when you remove the snowmobile cover. I figure that it'll keep bugs and mice out of the airbox.