I've installed quite a few of that kit (I'm a big fan of his front coils) -- Consider upgrading to JKS discos and new brake lines (longer=better - steel braid) the XJ's brakes are NOT over-adequate by any means, and Rusty's "brake-line extension kit" is only a good-low-buck work-around at best (no offense, it does get you to where things are safe, but I like "better" as a critera for stuff like brakes; you know you're gonna be adding tire diameter!).
Also, Rusty's HD Trackbar (from the 6" kit - like Stretch said!) with the frame mount will last MUCH longer and is only a few $$ more (the end and mount are the only $ difference) -- a good upgrade to get away from a common point of failure (even for stock XJs) - plus if you go up later, you'll be more than ready.
At 4.5" you will need to think about your driveshaft (more so with an automatic than a manual) -- you will be adding more vertical distance between the diff and the t-case output (say about 4.5") -- Nomatter how you look at it it'll be a "taller" triangle so the shaft will need to be longer (a 35" shaft if flat at stock will need to grow by about 1/3" for 4.5" lift) -- the tough thing is that the shaft length will be affected by your particular OEM characteristics, your net lift, and what kind of rotation you put into the axle (shims) or t-case (drop) so it's not something that you can hands-down disregard. Also, the opreating angle on your OEM slip-yoke is pretty inadequate (if you're gonna end-up drooping the rear much - as a result of longer shocks) - that can be addressed with the YJ's slip-yoke -- it'll offer more operating angle ( kinda like this pic
) and help a bit with the length. Not to scare you off of anything there, but getting the driveline right is important; definitely something to consider in all this.
I can say that in your vintage, the auto has a much shorter drive-shaft than a manual, so if you have an auto, then you'll probably have a little more work to do -- as a general rule a set of 3* shims (depending on AAL or leaf design), the YJ's Slip-Yoke, and about 1/8" of shim behind the LCAs' upper mount (depending on replacement LCA length) should get things covered for ya.
I'd offer a hand if Oregon wasn't such a commute!