Duane:

You can go either way on the tank system. I would visit my LHS or mail order store and get a nipple to go in the muffler. Not hard to do. Then run muffler pressure.

But so far as the fuel running out is concerned, it doesn't happen. The engine is pulling fuel from the tank. the tank has to get air to fill the space where the fuel was, so as long as the engine is running there will be a flow into the tank through the vent line.

The one big thing to watch with the K&B Sportster engines is the oil in the fuel. The Sportster is a plain bearing engine, there is no synthetic that will give proper lubrication to the crankshaft. Granted, it will run for a while with 100% synthetic, but for maximum engine life be sure to to use a fuel with castor oil as at least part of the lube mix. My choice is Omega, but there are others available.

Enjoy it.

Bill.