It was incredibly easy to replace the stern seat. All I had to do was buy a replacement web/wood seat, shear off four rivets that held the old tractor seat to the brackets, measure and cut the new seat. Then I lined up the holes with those already in the bracket for the front, but had to drill new holes in the metal bracket in the back, and secured everything with four bolts and nuts. Took me an hour working at a slow pace.
It's a bit more difficult to replace the sliding front seat. I'm told on Wenonah's the web seat uses a different size slider system so it's not as easy as taking off the tractor seat and replacing it with the web/wood version. I feel like you could remove the plastic tractor seat from the existing metal tubes that slide along the brackets, the fashion some way to connect a standard web/wood seat to those, but I've not tried myself. My wife, who mostly paddles in the bow, assures me she's fine with tractor seat so it stays.
Here's a few photos of the before and after: