What axle difference? In a stock configuration a lot of that matters, but when modded into a 4x4 the bulk of it goes out the window. Different springs, most likely different gears to accommodate bigger tires, if a D60 is used up front it's the same axle used between a factory 350/450, etc.
So the big question is is there any difference in the frames, and what difference between the rear axle/brakes.
In a lot of years in the F series the rear axle between a 350 and 450 was the same, except maybe C&C units, but not sure on the E series.