Your's are the most realistic! Kudos.
![](../../hosting.photobucket.com/albums/t461/165thspc/M4---High---Speed---Tractor/.highres/IMG_8368sm_zps7rueoi2t.jpg)
I just carved and modified the existing seat moldings to produce what you see in the photo - though they did not turn out as realistic looking as yours. I also have photo etched seatbelts coming, yet to add.
I would say mine look way "too perfect" and too big. The real seats were just flat canvas zippered bags filled with either folded blankets or stuffed with straw sisal (sp?) inside. Rough riders for sure but better than sitting on bare metal!