It's going to vibrate no matter what you do unless you can correct the angle between the pinion and the tcase. The only ways to do this are to lengthen the shaft with a dual case or by moving the axle forward. Or run the same length by running a hi-pinion diff...or drop the lift some. You can also shim the bejeezus out of the front springs to correct the pinion angle, but unless you turn the knuckles also, there goes your caster.
Jess at High Angle Driveline has had success in rephasing ujoint-ujoint styles to minimize vibration over steep angles. CVed will typically vibrate less, but you won't get quite as much droop out of it before it binds. With a single case, CVed 85 driveshaft (lengthened by Jess) and about 5.5" of lift on my 96, 40-45 mph is where the vibration gets really obnoxious and borderline undriveable. I'd stick with a CV if this is a daily driver and if you ever need 4wd on the road.
Basically, it's your angles that are the problem more than the length, but the angle is a function of length, so you need to sort out the rise over run to get things vibe-free.
Oh, and btw - your sig - better my momma than my sister and my sister's pretty good.
