I dont kno if you sorted this out yet but you need to split the tank open and create baffle plates. Then you need to add a basin that will house the intank pump. This is what I did for my duel intank pump set up
Tap a bung onto the lowest point on the gas tank. Run a line /fitting. Pass it thru a fuel filter then a external pump. That works fine. Using that setup in a Rb25de in a 280c.
Similar pump to posted above. Bought from hyper v same brand. He also has some excellent filters.
