Can I use a set of rear end links from a 4” lift on a 3” lift?

Are you referring to control arms when you say "end links"?

If so, only if they are adjustable.
 
If you're referring to sway bar links, the answer is "it depends". You would have to verify that the axle doesn't extend too far upward and bind the bar.

How much bumpstop extension do you have in the rear? If you have at least about 2.5" you'll likely be okay. (That is a guess and is not verified.)
 
If you're referring to sway bar links, the answer is "it depends". You would have to verify that the axle doesn't extend too far upward and bind the bar.

How much bumpstop extension do you have in the rear? If you have at least about 2.5" you'll likely be okay. (That is a guess and is not verified.)
My bump stop is for a 3” lift.