Noice job! I wish I had the money to buy welding equipment.
I'm surprised you can't fit in the air filter. Although I think you said you have a different carb, so maybe the filter that came with it is larger than the one that comes with the NT carb. You could either buy another air filter or maybe re-route the filter with some tubing,
kind of like this.
Also, if I were you I'd get a dual brake lever. I always hated having to reach under the clutch to pull the rear brake. You can get one off Sick Bike Parts, I think.