Yeah those are application specific though not sure how long or stiff they are as they are valved and packaged towards a specific vehicle like a ford f350. You would need a custom shock for a custom application. It's been a long time but I think you need a 6"-8" travel shock in the front with custom upper and lower mounts. Ruffstuffspecialties.com sells good mount options. The rear is 12.5? They are the short body versions so they fit on the factory mounts. Really best to measure your setup under multiple conditions and get the perfect fit at full droop, flex and rest. As far as valving i'm not real sure. The 7100's I had bought through 4x4parts got sent to Bilstein and came back with Xterra specific valving. The Fox shocks I bought on clearance at Polyperformance.com and had the guys there revalve them. Real nice crew there. I don't remember the valving I went with however.
Good points.
Every X is a bit different, and, what tires you run, the other suspension mods you have, how much armor weight you carry, plus typical cargo, etc, how high you lift is/your COG, and so many other things will change what will be "best" for your own rig.
For example, with a rig with 3" SL/2" BL and full skids, sliders and bumpers, on 33x12.5's, for rebound/compression, you started with OEM valving ~ 285/65 in front and 205/55 in back....with the front shock being a 9" - 13" travel and the rear being 14-23" travel......
....and you'd up it to ~ ~ 360/80 up front, with ~ the same travel (IFS), and 255/70 for the rear with ~ 16-26" travel.
Everyone's idea of "smooth ride" is different, with one guy's "rides like a 60's era caddy, like a dream" being another guy's "Rides like a 60's era caddy, it sucks". Some people want a more controlled ride, some like a floatier ride, etc. So, everyone's "perfect" valving will be a bit different.
If you raise the COG, you have more sprung weight, and you'd want more rebound valving to help control it. If you mount 35's instead of 33's, etc, you might want more compression valving to help control that unsprung weight, and so forth.
If you will run Revolvers, THEY smooth your ride out really really well, and, add enough travel that the 26" long shocks get stretched, and become your limiting factor....so a longer shock that can stilll get short enough is needed, and so forth.
The FRONT, being IFS, and the shocks being so far inboard, mean you need almost no travel to cover the arms droop/compression cycles...and a few inches of wheel travel is covered by less than an inch of shock travel, etc. (~ 4-5" of shock travel will cover most UCA based lifts)
Another thing to consider...the 5100's for example are very tough as far as over extension and compression...so, if for example you hang the axle by the shock (Shock is limiting factor in droop for this scenario), the 5100 can take it. The 7100 is not built the same way, and over extension can damage the shock (Ask me how I know...)...so while the 7100 has great performance, you do have to make sure you do what Silver mentioned, and test droop/compress the rig's suspension to see just how close the upper shock mounts get to each other, and how far away, etc. (You do this with the shock's disconnected)
When doing the front shock mounts, note the reference points, as the top's a stud etc...so you want to make sure you can translate the mount distances to other mount types later. On the rear's, many of us used Skidderz, etc, or otherwise changed where the lower shock mounts were, to improve rock survival, etc. This changes the needed shock lengths proportionally. If also moving the top mounts, well, its ALL different.