I am installing an add-a-leaf to my 99 tacoma and we took the axle down and the springs apart before we noticed which side the long side went to....any help?

 

if they're anything like my 91, the long end is towards the rear.

 

Yep, center pin is typically offset to the front, so the rear half is longer. Easy enough to check by putting the spring in the hanger and see if the center pin is about in the middle of the wheel well, or just look for the end of the spring with the military wrap (2nd leaf wrapped around the main leaf) and that end goes in the hanger.