slight shackle lift

I was looking to install replacement greasable shackles for my stock 3B that have a 1-1/2" lift to them, thats not big enough to really make a difference with angles of components. Is it?http://www.rockymountainsusp.com/W_shackles_Jeep.HTM

 

You are right to be concerned.
The best answer is to measure your castor, before and after.
Straight axles tend to be factory set from 2.5 to 8 degress somewhere in the middle is a good goal.

The longer shackle will tip the axle forward and reduce castor.
If you only have 2.5 or so to begain with then you are going to have a problem similer to a shopping cart wheel that shimmies really bad as well as no return to center after turning.

You can buy a degree wheel or angle finder at H depot with a magnet on the wheel. I paid 7.00$ for mine try to stick this on a flat spot like the bottom of a ball joint to find you current castor angle. Keep in mind this should be on a flat surface with the normal weight on the wheel.
If you have to take the tire off then put a jackstand under the axle near the hub at levale height.

 

I personally wouldnt go over 1/2" shackle lift (1" over stock) but thats just me who has a 2.5" lift spring. If you are doing stock springs then prolly not an issue cept for changed steering geometry.