If you decide to keep your tank and add the manifold connecting all the vent hoses, MAKE SURE to get the hose clamps extremely tight!! I have seen a puddle under the back of my car.
Regarding the fuel cell, do you have to lose the spare tire and tub to install it? Per your link, Jon, with the filler neck right on top, it looks like either that, and put it where the stock tank was, or raise the center of gravity and put it on the luggage deck. :dunno: