i've just taken out the IVG on it and done the same with my trilogy cocker, and the spring is much larger on the u/l (it sticks out the body by 1cm and the trilogy is shorter than the body by 1cm)
EDIT: also i replaced the actual screw, with my trilogy screw, and it screws in about 3 more threads almost without any friction, and the u/l almost tears the threads off the inside of the trilogy as soon as i start screwing it. Surely they made them using the same threads!?!