If I remember right the big boss seat isn't as long. It looked like they just took a standard ATV seat and cut it short. You could do the same by removing the rear of the cover, cutting the pan and foam and then re-stapling the cover. I agree the front portion of the seat is the same.
Trail Boss seat on Big Boss body - Anyone tried this?
I am trying to restore to a good useable condition a 1991 Big Boss 6x6 250. I bought it without a seat, and it seams the seats are nearly impossible to find, even at salvage. Has anyone ran into this issue and tried to retrofit a TB seat onto the frame? I don't have exact measurements, but it seems you would only need to bolt on or weld a couple tabs for the seat latch on the rear of the seat to hook onto, instead of wingnuts to hold it down like what the BB appears to use. The front airbox and shroud mould appear to be the exact same for both seats. Any advice would be greatly appreciated so I can finish this project and go explore the great mountains in Colorado!!!! 
Cheers
Cheers
