2018 350 XLT 3.5L
I had the floor up awhile ago on a failed project and tried to make it productive by taking some general measurements of seat rail and bolt locations for my 15 passenger 2018 148". I realized I never shared this, in case it helps somebody. Not sure how consistent spare tire mechanism or other measure point is from vehicle to vehicle so use measurements at your discretion. Horizontal lines are seat mount locations, points are bolts. Picture of setup accompanied. I think it may be the same for other model years, but can't verify.