I think its a bit more complicated than that....."Centre of Gravity" is one thing, but you are actually putting that weight to ground on four points - the wheels....so what are the corner weights, and how far are the furthest corners away from the pivot point of the tail-lift? You'll then have to do some maths to work out the leveraged weight you are putting onto the structure of the tail-lift.
Of course you can make all Health and Safety practitioners scream by saying that rated capacities usually have at least a 100% safety factor built in so you'll probably get away with it