First, Phil, welcome to the ALR site. I think you'll be pleased with the feedback you get here...there are many very talented builders who frequent the site, and are happy to share their experience and knowledge.
I am familiar only with TOW's offering for precarved stocks, but it is likely that they are all ok with minor changes in architecture. I would recommend that you buy a swamped barrel rather than a parallel one, because that one thing along changes the beauty, grace, and balance of the rifle. As far as length goes, that is only personal taste. The 31" barrel will be just as accurate as the longer one, notwithstanding the increased sight radius of the longer barrel. I have a jaeger built around a Getz .60 cal barrel and it is my favourite hunting rifle...light to carry, quick to the target, and deadly accurate. I built mine with a piece of good western maple and very much like the blast of colour in the figure of this wood. The only original rifle or gun I've ever seen stocked in oak was a re-stock by a farmer...it was terrible. Most jaegers were stocked in European walnut, so English walnut would be the best choice, as far as I am concerned. Maple, cherry, and Black Walnut are also fine hardwoods for stockmaking. But not oak! IMHO