Why J shock mod. question

i had to relocate my rear upper shock mount down about 2.5"-3.0" due to rust,,in other words the shock was wedged between the muffler heet shield and the frame because the upper shock mount TORE AWAY from the frame!

here is my question. because i moved the mounts down, do i need to get shocks that have a shorter extended/collapsed length?

common sense tells me yes, but i have had a couple people tell me no...the jeep needs new a suspension could i lift it 2.5-3.0" and stay with oem length on the shocks?  

You don't want your upward suspension travel stopped by the shock being fully compressed. That destroys shocks and shock mounts. It is your bump stops that should limit your upward suspension travel.

For an off-road vehicle, you want the longest shock possible, and then lower your bump stops to protect the shocks. Obviously, there is a compromise between bump stops and shock length. You don't want to be left with only an inch of uptravel before you hit the bump stops.

The worst way to fix your upper mount was to move it down. You may need to get up in there and cut out the rust and weld in some patches. You should also consider relocating the shock, both upper and lower. There are lots of relocation options that a lot of guys do to get longer shocks. The rusted out shock mount may end up being a good thing in the long run because it will cause you to improve upon the original design.