Just make sure you've got ways for air to both enter and leave the tank before the vacuum or pressure reaches levels unhealthy for the system. If you simply remove the vapor/liquid separator tank and just cap everything back there, you're asking for trouble (even if you've got a later style gas cap with the check valve). You'll be OK for vacuum, but pressure will still be an issue.

 

And simply connecting the nipple on the tank that used to have the "orange" hose on it to the nipple on the filler neck won't do anything to relieve pressure or vacuum. It'll enable you to get more fuel in the tank at the gas station, but it won't do anything about vacuum or pressure buildup.

Oh, yes, I'm going to use the 3/8 nipple on top of the tank as a vent.

Gotcha. That will work to vent the tank (in both directions). However...

 

A concern about doing it that way is that you're going to smell it since it will vent into the passenger compartment.
 

Oh, yes, I'm going to use the 3/8 nipple on top of the tank as a vent.

Where do you plan to route the hose for that vent to prevent fuel from sloshing out during aggressive cornering? Just curious.

Where do you plan to route the hose for that vent to prevent fuel from sloshing out during aggressive cornering? Just curious.

I'll connect the vent on top of the tank to the evap canister line going to the front of the car.  The canister is gone, but it will move the vent away from passengers and keep gas from sloshing out.

My tank vents via the carbon canister line. The canister itself is gone but the line is there and runs from the tank in back to the engine bay