What are the overall benefits of torque boxes? I know they stiffen it up alittle, right, but anything else? I have a drivers one and just wondering if I should invest in installing a passenger one.

 

No one? Neither of the FAQ links work...

 

You are correct. They are there to strengthen your uni-body. They actually act as a gusset. Ford engineers designed the torque box to add structural support to reinforce the weak design of the uni-body.
In my opinion, they should have made it an open design as not to trap moisture and dirt resulting in massive rust and frame failure. I guess they didn't look 30-40 years down the road.

 

They aren't much good in a high torque, high horsepower Mustang that frequently drags with slicks. They are only spot welded in and will twist right out under heavy power situations. You have to weld them in with a seam, and even think about getting a kit that will strengthen them. Here is an article about how to put them in a 65-66.
http://www.mustangmonthly.com/projec...ng_torque_box/