I don't have one of those. My drive lines have 4 bolts and u joints on each end of them.

 

I have the roto flex on mine and was wondering if it would be an easy fix to replace this part?

 

Depending on the tyre diameter and the diff ratios (3.54's in the 95 D1) your in the vibration zone of a out of balance driveshaft. More of a shuddering vibration.
Not only the roto flex joint, actually called a Giubo (PC) taking care of rotational torque, there is a pilot pin which also centers the driveshaft which has a hard rubber insert with hole for the pin to keep the driveshaft in alignment. Besides the roto coming apart the pin keeps it centered unless the rubber bushing is worn and falling apart, bingo vibrations.
Bad enough those POS roto joints lasting under normal use, harder multiplying high torque in low range about tearing them apart.
Another enemy is your added angle of deflection with that 2" lift now shortening the roto's life..
The rear SWB range Rover driveshaft fits right in a direct replacement having a real steel U joint. Usually comes in kit with a 4 bolt flange replacing the 3 bolt for the roto joint plus a new oil seal. Easy replacement with normal tools, a torque wrench plus an inch /lb wrench unless you have the "feel" for pinion gear preload. Rather hard to detect with ring gear attached but better than not knowing the amount of preload. This will solve your vibration problems. Went through a couple roto joints, my driving style is not your grandmother's driving I ripped them apart within 500 miles, stopped wasting money then purchased a real driveshaft. Wait until Atlantic British or some other sources has a holiday sale as they are not cheap but almost bullet proof and smooth no more vibration problems. Talking 19 years same tight U joints, lubed at every oil change, all other ball joints and tie rod ends lubed every other oil change. Modified joints now all having zerk fittings. All still tight at 142K miles......~~=o&o>........