The 3500HD has the same coil suspension as the 4x4. As far as the F450 2wd I'm not sure but I do know the F350HD that we have at work has the same spring pad width as the F350 4x4. The Dodge 3500HD even uses the same inner and outer knuckles and spindles as the D60 used in the 4x4.
Wrong! The 3500HD only came as a 2 wheel drive and had a strait front axel with leaf springs. The 3500 2x4 has independent with coils and the 3500 4x4 has independent with tosion bars.