Sounds like you have covered most all of the bases getting this ready to ride. I don't think that the headlight problem is related at all to the bogging issue. The lighting coil on the stator is an entirely separate circuit from the ignition circuit. It sounds like your keyswitch and it's connection is OK since your other lights work. The problem has to be from the the keyswitch or dimmer switch to the headlight, or the headlight connection.
I'm trying to think what areas I would "Revisit" if I was in your shoes for the bogging. It sure sounds like your getting too much fuel in the mixture if a squirt from the primer, or giving it some choke, makes the bog worse.
Like "kawhead" mentioned, those little o rings in the carb have to seal perfectly to the needle jet and the float bowl, or they will leak fuel through the main jet circuit. That may be the 1st thing I would check, if there's any doubt in your mind.
Is a choke plunger hanging up and not returning down to the fully seated position with the choke off? You should have about 1/16 inch of play on the plunger cable with the choke lever off.
A carb needle and seat leaking by? Probably not, but worth a look.
Is a float hanging up, even though you cleaned the carbs? Do you have an in-line fuel filter in the system? Sometimes some crud from the tank can mess up all the time spent cleaning the carbs.
Could your new gas have some water in it that settled to the bottom of the tank in the time since you filled it? Probably not, since your sled is starting and idling OK....but...?
One more thing to try, if you haven't done this. If your bog is fuel related, this won't help, but I have seen it cause some strange running issues. Unscrew the spark plug caps from the wires. Trim the wires back about 3/8 inch and firmly screw the caps back onto the fresh wire. This loss of a perfect connection over 35 years can really make you scratch your head over spark issues. It's easy and takes 5 minutes.
Just some thoughts of things to try.
Good Luck!