You should measure it with all the weight you are going to have on the frame. So in its natural driving position. If you measure it hanging down it may change when you add the weight and start driving, then you could have some serious vibration. I think there was a good thread on here not too long ago about setting the pinion angle. Do a search. Good Luck.
what you do is get yourself a mechanic to measure that for ya'. just funnin' ya', good to see you and the missus' on saturday. the folks from the gas station above Fuzzy's came looking over the guard rail to see what all the smoke was from,(your burnout), freaked them out i think.