E-Bay has a whole new seat for the JD 790 for $169 and free shipping. And it's a taller back than the original. I'm leaning that way rather than having it redone.
I have replaced many seat cushion sets over the years and have been satisfied with the OEM stuff. OS tractors in particular are subject to alot of weathering regardless of actual use from what I can tell. Covered parking really helps with that.