I have greasable urethane bushings on my K20's springs and regular urethane for the transfer case mount and body mounts. I have the greasable urethane bushings also on my K5 along with the regular urethane mount for it's transfer case.
I don't have any squeeking. To be honest I don't think I would be able to hear any squeeks on the K20, however the K5 is alot more quite and I don't have any squeeks.
I got the greasable bushings from
www.offroaddesign.com