I am running 'supposedly' 3" 400kg constant rated coils in the back - Dobinson units. They have not survived the lift or height configuration to be honest, car is no doubt heavier than the rating of the coils, however with the coil assistance I am happy with the overall ride and articulation for the limited stuff I do. I would contact BOSS and ask the question. I think the 2 pack airbag is the recommendation for standard to 2". I have used the bags on one occasion to jack the rear up for a ground clearance issue - cannot remember the specifics of the 2 V 3 donut selection - too long ago
Mine is trimmed to sit level when loaded.