Not great pictures but what I found in my collection.
1973-1976 long jump seats. slanted at the front to accommodate front seats, single armrest, no leg, rest on bump stop. Note that up to 74 the frame was painted gray/metallic and from 1975 black.
View attachment 3180783
1977 to ? long jump seat, I call them the hybrids as they have both the bump stops and a leg, they still have the single armrest also.
View attachment 3180782
Note that the leg is recessed in the seat (sorry not easy to see in my dark pictures), so less cushion thickness... This allow to chose if you want to use the leg or the bump stops, both work. Leg is also lock in place, you need to slide it toward the front to unlock it (so it's not falling if you don't use the leg).
View attachment 3180784
I would agree they look weird, but there is also no armrest so not a pre-leg version AFAIK.
I always thought the armrest served the purpose to stabilise the jump seat on no-leg version as you create a torque force seating on them.
79+ in light grey went leg only design and no armrest, but I'm not too sure how were the 78-79 long bench seats as it was hybrid/evolving years in this area.