for 31x10.5's I would say go for a good 3.0" lift. You will want a set of 15"x7" wheels with 3.75" to 4.50" backspace or 15"x8" with 4.5" to 4.75" backspace if you want to keep the tires from rubbing the lower arm when turning.
I ran the 3" with my old 30x9.5's for over a year, NEVER rubbed on the body, but with stock wheels they did rubb the lower arms (tread lugs hitting at full turn), aftermarket tubeular arms would have fixed that.
I did my lift in stages.
1- Rustys basic 3" HD kit with rear add-a-leaf (3.5" front + 2.5" rear)
2- 0.75' rear shackles for 3.25" rear (I should have got the rear spring packs)
3- 1" transfer case drop
4- adjustable front tackbar
4.5- added 32x11.5's = lots of rubbing (did a little trimming)
5- replaced stock(short) #2 leaf with a home made full length #2 leaf (gained 1") now at 4.0" total rear.
6- added 0.75" front spacers to level it + Rustys upper & lower arms + brake lines (4.25" total in front)
I should have just gotten a full Rustys 4.5" kit with full rear springs & arms to start with. But that would have been alot of $ all at once. I did this over about a 2.5 year time.
BEST bet.... if you don't want to keep "playing" with the lift. Just get the 2" spacer kit and 30x9.5's. When you go past that, it never ends
.
NEXT is a 6"-7" long arm kit (Full Traction) with Bushwacker cut-outs & 35's
.
Then D44hp front & 9" rear... see what I mean, it never ends.
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LOST in Oregon
'04 KJ sport, Rustys spacers front+ Skyjacker coils rear,16"x8" Rubi's LT245/75R16 BFG A/T, Mopar skids & hooks, Reese Hitch.
'96 XJ sport, Rustys lift NOW 4.25" with arms, NOW 32x11.5R15 muds, Rustys hooks, Valley Hitch.
http://www.cardomain.com/ride/2273596
'78 Z-28 & '96 Metro