Well welcome to the site, nice to know a little about the person im/we are talking to.
For starters the fuel tank will be difficult to change for a smaller size due to the Dragstars frame having a double back bone (not single like Harley's and other bikes) i know this as im currently changing my fuel tank too, so the way im getting round this is by using a Harley Davidson duel (split) fuel tank if you look at "My Bobber project" you can see all the things that ive done and see how it will look like with a smaller tank set up.
What is this problem you have with the Air intake and carbs?
The only way you can get a KJS manifold is if you strike it lucky on E-bay as if they don't make them any more then you aint getting one, or the other option is to get a single carb and have a good mechanic to fabricate a way to mount it to the Draggy.
Good luck and post up some pics!