As far as I know, the gas ones were the smaller pistons and the KD versions the larger. High altitude versions may have been fitted with the larger pistons, too.
There may be a difference in head height for the different compression ratios, so push rods may be different length (valves will be). Manifolds for the KD are deeper, too, but not much use for the above, necessarily.
But all that said, the liners and pistons could have been changed at some point - although less likely on these older tractors, I would have thought.
You could compare the parts book item numbers for each model.
The alternative to pulling the pan would be to remove the head! Or you might be able to get a measurement through the crankcase inspection covers.