if this is primarily a street truck, i'd say use the spacers. They are already there you only need to move them from over the frame to between the frame and the crossmember. when you shim the axle, it changes the geometry at the pinion and you should try to counter that at the t-case output in the opposite direction. The operating angles of the 2 u-joints need to be equal and opposite so as to cancel out any vibrations. So as the pinion comes up, the t-case output should come down. Ideally you want these moves to be equal and you could check with a magnetic angle finder, but that really should have been done on the pinion before removing the old springs.
spacing the t-case down may also save you the cost of extending the driveshaft (over $100 by the time you add in balance and if u-joints are replaced).
As 4x4Freak stated, the yokes on your driveshaft can not be out of phase, so don't worry about that one.
I removed my sway bar (also an 84 blazer) when I installed my first lift (4 inch pro comp) and never regretted it. it was not a daily driver, but it was driven on the street frequently, and for some fairly long trips to go wheeling. make sure you've got good shocks and you'll be fine, but do be cautious going into turns as you will have more body roll than you used to. finally, if you decide the body roll is too much for you, check out the ORD disconnects (
http://offroaddesign.com/catalog/swaybarkit.htm) which will allow you to run the sway bar with your lift and also quickly remove it from the picture when you are ready to head offroad.
