I don't have a clue on length, but you want the rear axle pinion to point slightly below straight through the driveshaft. I use a magnetic angle finder like this one: Wixey Digital Angle Gauge Type 2 with Magnetic Base and Backlight: Amazon.com: Industrial & Scientific. With the vehicle on all 4 wheels under it's own weight put the angle finder on the driveshaft lengthwise either at the very bottom (6 o'clock) or very top (12 o'clock) and zero it out, then remove the driveshaft from the rear pinion and place the angle gauge on the pinion flange vertically (the display will face either 3 o'clock or 9 o'clock), adjust your upper/lower control arms until you reach 88 (or 92) degrees. Make sure you jounce/bounce the rear suspension after each adjustment.

EDIT: Drive Shaft Angles Explained - YouTube 4wd driveshaft starts around 7:30