I am finishing up work on my 915 08 box. I wanted a close ratio set-up, so I swapped out my second, third and fifth gear pairs, and 'flipped' my existing third gear into the forth gear position. I follow Peter's instructions closely. Especially about cleaning every part and reinstalling them dry. Unfortunately, once I torqued down the covers, I found resistance and binding when I turned the main shaft by hand. I thought perhaps the shift forks were rubbing against the sliders. I measured and found 5 mils of run out on my sliders. After milling off 5 mils from the inside of my shift forks, with no reduction in binding, I next used a small paint brush to introduce some gear oil such that it would seep into my 'free' gears and coat the needle bearings within. Bingo! No more binding. Now, my issue may have resulted due to the fact that my bearings had some miles on them. (Though I fully renewed my gear box less than 10,000 miles back: bearings, friction bands, dog teeth, sliders etc, etc..) Also, while I 'flipped' my third gear into the forth gear position, I maintained the orientation of its needle bearing cage so as to keep it spinning in its original direction.
I wanted to mention my experience in case Peter had feedback for me, or if it might be helpful to another amateur transmission builder in a similar bind.