when doing this, im assuming that youre doing so to raise the back of the car up a bit. much like the air shocks did. the coil overs will work, yes. work properly, probabley not. when you do this, all the weight of the car will effectively be resting on the shock mounts, not the leaves. the leaves would be more along for the ride and axle location at this point. you will see some handling benifits due to the higher effective spring rate, but its hard to determine what that rate will be when using both.
reason i know about this is that a while back, i was running some of those parts store coil over conversions to do the same thing on my duster. it did work, but i broke shock mounts after a while, killed shocks, and had some twitch handling.
hope this helped. if it were mine, id do what i did and get the springs i need from ESPO, and be done with it. the sprongs have been in for 5 yers now, and have not sagged.
Michael