If strange rated your drive shaft, they should already included the factor of safety. If they took twenty percent, and then you do on top of that....You could really be selling it short. I don't know that, but might be worth calling and asking.
That jaunt was in my 5.2 Dakota. 3.55 rear with whatever overdrive ratio a 727 has.
I'm really curious to see how this turns out for you. Drive shaft failure scares the hell out of me! At least you know it's not tires!
