Thanks for the good input. I've probably driven 2-300 miles before I changed the transmission and noticed the loose nut. Here's what I think I'll try.
Remove the wheels and tires and tighten the nut until the rotational pull is at the upper end of it's spec. Maybe the upper end will compensate for the drag of the axles. Then tighten to the next cotter pin slot.
It's a 4.56 so I want to drive a few miles to see if the 0.72 overdrive gets me around OK. I'm not planning on doing any freeway driving with it. If it's OK then I may pull it out to check it properly. If it's not I'll run it till I find a lower ratio pumpkin.
I also just installed 3 point seat belts, if they work out I'll take some photos when I take them and the seats back out to paint.
