We made a number of mods to the bench seat on our 2120SC. First, we didn't like the hatch access, so we made it so you could remove the top cushion to stow stuff from the top. We thought about hinging the top, but that presents a lot of problems, so we just installed wood strips on the bottom to make it stay in the right place on top of the box. While doing so, we raised the front of the cushion to give a little more thigh support (later Parkers have a raised bolster on front of the cushion that helps in this area). We still felt like we didn't have enough cushion under our legs, so we moved the box out towards the centerline of the boat about three inches and made "shims" to move the backrest back the same amount. Altogether it made the seat more useful and comfortable. Pix on my website.
Since we moved up to the 2320, we haven't made the same changes. For one thing, it has the built-in tackle trays, and it has the improved cushion design. Time will tell if we do it all over again.