LS evap system?
 

What are you LS guys doing with your evap system?

There is a valve and line going under the throttle body that runs I guess back to the Fbody gas tank. Do I pull that or use it for something?

Although not emissions correct, a lot of people just plug the charcoal canister vent line and eliminate the canister. That works because the fill cap has both an inlet check valve and a redundant/safety pressure relief valve. The relief valve has a higher pressure setting than the one in the canister line, but not so high that it's unacceptable. One consideration, if you replace the EFI with a carburetor the needle and seat must be in good condition. Otherwise, pressure in the tank may flood the carb and force out fuel.