Toby, Sargent can reuse the stock seat cover, no problem. I had mine refoamed with the "super cell atomic" foam and love it! A big improvement on comfort and support. Came back looking just like when I sent it down to them. In fact, the one, very minor complaint I have is that I wish they had "foamed" it as a true "plank" seat. They followed the contour and my smooshed addition to it a bit more than I would have liked. But it is still great!
Navigating their website and order work sheet can be a bit confusing. I called down and talked to the head of the "seat work division", I believe his name was Bob (not sure, I wouldn't swear to it), very helpful, explained everything and walked me through the paper work.
Also, check the "web specials" section of the website. They have a coupon for discounts on seat work quite often.