My wife and I have been building our home for five years. After 2 years
on subfloors we had our recycled flooring milled and prefinished with 3 coats urethane the last coat containing aluminum oxide. This yielded 3/4"
tongue and groove(along length only) finished material in lengths from 3-12 ft. and widths from 5-9 inches. When inquiring about installation we received many different recommendations:
1. Screw and peg (whoops prefinished)
2. Nail using biscuits on ends (seal bottoms with urethane applied by roller 1st.
3. Staple and use an adhesive. ????
What would be the preferred method and is any underlayment necessary?
Additional info.... Material was resawn from 15.5" x 9.5" x 20' timbers, most likely longleaf and came from a bldg built over 100 yrs ago. I counted 350 rings and the moisture content was less than 5%

I would screw and peg. Prefinish your pegs & with a color match filler, if needed.

Once you get past 5" wide, the more it will want to cup, with the slightest imbalance of moisture content.

5% MC is very low!! do you live in AZ. or CO., where it is always arid/low humidity??

Screw and plug is a way to do it. However, Carlisle Restoration, who manufactures all types of wide plank floors, specializing in wide pine plank, does utilize the glue and blind nail method. I installed 5000 ft of 12" old growth antique heart pine from Carlisle. We glued it with PL400 (per Carlisle's instructions) and blind nailed it every 8" with a Bostitch M111 FS. Went back 5 years later to recoat the kitchen only. The floors looked AWESOME. No cupping, shrinkage, separation, gaps, buckling, etc. The reason for a recoat is the original finish was Waterlox. And it was scuffed up and needed attention. But the floors were holding up very well. I was surprised at how little denting there was. But this was old growth, antique all heart pine. Supposedly as hard as oak. And by the looks of it after five years, I'd hafta agree. We did not use any underlayment but did have a vapor retarder installed in the crawl space. We acclimated the flooring for two weeks inside the home prior to beginning the install. Each board was "stickered" so as to allow better acclimation. I would not hesitate to use this method again.