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Shocks are designed to work for specific lift heights - or more importantly, specific bumpstop heights. This means the compressed length of shock must be able to fit without bottoming out. You can imagine if you're bottoming out the shocks, and not the bumpstops first, then all the stress of the axle coming into contact with the frame rests on the shocks...this destroys the shocks and shock mounts.
As long as the bumpstops limit the axle uptravel before the shocks bottom out, the lift height just determines how much uptravel vs downtravel you have.
Stock shocks are:
Front: ~13" compressed length
Rear: ~12.25" compressed length
If you buy a shock that has longer compressed length that these, you'll need increase the bumpstop extensions by the difference (which reduces uptravel).
2" lift OME shocks are part numbers are N66 and N67.
N66's have a 13.5" compressed length - which is the very max you can fit in the stock mounts, so they will fit without extending the bumpstops.
N67's have a 13.5" compressed length - in the rear, this means you need a minimum of 1.25" bumpstop extensions. Thats from 13.5"-12.25" = 1.25"
So, if you don't have any lift at all...you would need to lose 1.25" uptravel in the rear to run the OME N67 rear shocks.
On the flip side, if you add a 2" spring lift, you actually gain 0.75" uptravel over stock.
If you add a spacer lift (budget boost), you don't gain any uptravel because you need to install bumpstop extensions the same length as the spacers, because the spacers reduce the amount of space the spring has to compress into.
So, if you're not installing a lift, then stick with stock length shocks. Bilstein "HD" 4600 series is an example.
Read here for more:
http://www.wranglerforum.com/f5/correct-bumpstop-length-70047.html