I have zero knowledge on the swap. I will say the 4WD light on my 90 hasn't worked since I bought it, haven't missed it.

 

At 3.5" of lift, I actually didn't have that many vibrations, but at 4.5" of lift I put in t-case drop spacers and had minimal vibrations.
Then I swapped the 8.25 for a Ford 8.8 and had horrible vibrations. The shaft was too short and I think it caused too little spline engagement at the t-case which caused bad vibrations.

Installed the Advance Adapters SYE in about 5 hours with the t-case still in the Jeep(minus the trip to Sears). Buy the good set of flat-nosed lock ring pliers and its easy.

There is a chart somewhere with compatible double cardan driveshafts and measurements. My manual trans XJ uses a longer shaft which I pulled from a 2003 WJ. It was double cardan and longer than the ZJ shafts I looked at. Working great but it's still 1.5" or so short so my driveshaft shop actually scrounged up a longer yoke section (on the axle side) which still uses a 1310 joint. Whole assembly balanced out nicely but if I were to do it again I would just order a brand new custom driveshaft to length and avoid the hassle. $230 (last time I checked), not that expensive all things considering.

 

1987 Jeep Comanche on 3.5" front, 4.5" rear. No SYE needed because our driveshafts are longer than an XJ.

 

1993 XJ here, C8.25, 231, 3.5" lift and no vibes. I had some minimal vibes when I first installed the lift but they went away completely in a month or two. I guess I got lucky.

 

1998 Xj 4.0 ltd RHD. NP242 D30 front, D35 rear.
3" RC lift.
Vibration City!
Replaced knackered rear diff carrier and pinion bearings - much better
Replaced front diff bearing - bit better again
Replaced UJs - teeny bit better
TC drop - not much better
SYE and (luckily I can) a front prop shaft on the back - smoother than Silky the silkworm in his best silk pyjamas!
TC drop taken back out - Silky still in his PJs!

 

1994 , 4.0 ,aw4, np231, sye , adams driveshafts , Dana 30 front with spartan lunchbox locker , ford 8.8 rear with Yukon grizzly locker , 4.10 gears , 5” lift , 34-10.50-15 super swamper tsl tires , it is long armed up front , clocked t case , tummy tucked , and has shackle relocation boxes in rear rides like a dream after the tires warm up lol

 

This thread is really pointless...each rig is different, and it will sometimes take some trial and error to get things right.

Some people have had to do SYE's at 2.5-3.5 inches, some not at all at that height.

The best advice I can give is to research as much as possible as to what works for most, make a decision where you want to go with it, do it, then go through it if there's issues.

FWIW, I'm on 5.5" of lift, RE coils and leafs with 4*shims, Bilstein 5100's, D30/8.25 with 4.88's, Spartans, on 35's, with SYE.

 

99. aw4 np231. NO SYE 2" no vibes, 3.5" no vibes, 4.5" slight vibes; installed degree shims and it went away. 5.5" with shims, very minimal vibes at 55mph.

96 AW4 , NP231, NO SYE, 2.5" NO VIBES

90 aw4 np242 NO SYE 2.5" no vibes

90 MJ, ax15 NP231 NO SYE, 4" no vibes. 4.5" slight vibes, 6.5" very minimal vibes

 

1998 XJ w/ 4.5" of lift, AW4, NP242, 1" t/c drop, no SYE, 4.10 gears, and 35's. I get very very slight vibrations at 40-50mph when on throttle. The vibrations are so slight that I didn't even know I had them until after I switched from MT/R's to BFG KO2's. I'm running 3" OME springs in the rear with Clayton shackles. The shackles obviously rotated the pinion up creating what should be an undesirable pinion angle but somehow its smooth. I cant explain it. I do plan on installing a Advance Adapters SYE in the future but thats just to get rid of the t/c drop and ensure I'm not going to lose the shaft when articulating on the trail.