I purchased 650 s.f. of Bruce, pre-finished, 3/4"x2 1/4", solid wood flooring and had a local contractor lay it. Here are some points the contractor made:
He wouldn't lay the flooring over any sub-floor but plywood. Builder's paper was needed between the sub-floor and the finished wood floor. the floor was nailed in the conventional manner just like a raw wood floor. The floor needed expansion room at the edges.
The floor has been down about 6 months. I remains beautiful and we are very pleased. We purchased the flooring from the contractor rep of a large local flooring company for $2.93 s.f. The installer charged us $1.50 s.f. After watching the installer I'm glad I didn't try it myself. I'm relatively handy as a DIYer but in this case the learning curve would have been significant and possibly costly. He did it in a weekend.