My comment was based on the comparison of the two tractors in the original post, and I have not looked at the smaller size JD and NH you mention here, so I'm not sure how they are built. What I meant was that Kubota uses a fabricated steel frame on the B and BX range, much like that on a truck, to attach the engine to the rear axle and lift assy. This allows certain advantages in packaging, and keep the weight down. The 1428v has large castings, gearboxes etc., that attach the enginge to the rear axle assy. - this is how most all larger tractors have been made, and accounts for the increased weight. There are advantages & disadvantages to each method, it is just a difference which is worth understanding. The BX has a steel frame, as does the GC2300 I think, but you'll have to look at the JD & NH to be sure about them. The sub-CUT's are all pretty light, so I wouldn't be surprised if they're built with a fabricated steel frame of some kind.