i just got some new illuminas and it didnt come with bump stops so im just going to re-use the ones off my agx's but they are pretty damn short like 3/4 of it is cut off does it matter how long it is?

 

Depends how low you want to go relative the length of your shocks.
Install the shocks only without springs.
Jack up suspension to the ride height you want.
See how much travell you have.
If you want more at that ride height make them shorter.
If you want less make them longer.
Make sure you dont get carried away with suspension travell.
Go for around 20mm-40mm depending on ride height.