mounting 31"s on a 97 4 door
 

what is the easyest way of mounting 31's body lift? torsion bar ?

You need to search and you will find the answer, buuuuuuut since I just did it I can quickly let you know. You will need a 2-3" body lift and a slight torsion bar crank with some 2" shackles. Many will tell you that you can get away with less but I just finished this and put the 31's on two days ago and they still slightly rub at full lock. If you do any amount of offroading this will be the least amount of lift you will want to run 31" tires.

You could also get aftermarket wheels with an inch or two less backspacing but then I am sure you will be trimming into the body of your truck and depending on the condition that may not be a wise idea for resale purposes. If you can get a 3" body lift go with that, it raises center of gravity of your vehicle so you have to take it slightly easier making quick manouvers at high speeds but so will any lifting of the vehicle. The best way obviously to fit 31" tires would be a 5" or 6" $1500-$2500 lift kit that actually lifts your frame and body but you probably don't want to spend that much only to put 31" tires on it:)

Cliff notes: minimum 2" body lift, 1" Tbar, 2" shackles - cheap way to run 31" tires and they will more then likely rub at full lock, make sure you get an alignment after getting the tires and installing the lift or your new tires wont be new for long! Oh ya and make sure you get pictures!