No there not.
3s 4s 5s all have two sets of gears in the lowers & two
vertical shafts. 3s&4s came with either small or large prop
shaft. ( 19 spline or 26spline) The 3s were used on mostly
V hull design because of there longer X height,4s were
mostly used on cats at the surface with a larger prop shaft &
shorter X dimension.5s are are much like 4s but with larger
bearings and shafts.There Gimbel will also support more HP.
Same with 6s but the big advantage is that steering is built
in the gimbel assembly.Parts for 3s& 4s are getting hard to
come by.I'm not totally sure but I think production of the 5s
will also be coming to and end. All great drives in there time.