I know it's been done on XJ's, but I wouldn't do it. JMO...
The front coil set-up can be made to work so well with CA drop brackets or long arms, etc that I don't see the extra work and expense to be worth it at all.
The approach angles on the front leafed XJ's I've seen were bad too, and they won't outperform a good coil set-up in front.
Back in the day, a local guy here built a leaf front set-up on his XJ with a 10" lift. (we thought that was cool back then...)
He was running 33's. (on a 10" lift- YUK!)
My XJ had 32's on a 5" lift, and my approach angle was better than his...