you need to measure and have a shop make you a shaft that fits. you could just cut down a XJ shaft, but it would still need to be balanced, there is no set length for a shaft, there are so many variation in drivetrain lengths that there it would be nearly impossible to have someone say you need a XX long shaft.
measure from center of u-joint cap to center of u-joint cap at ride height
measure from center of u-joint cap to center of u-joint cap at full compresion
measure from center of u-joint cap to center of u-joint cap at full droop
you will also need to know what joints you have and where the slip shaft is going to be located, in the out put of the tcase or in the shaft, do you want a CV shaft or a traditional u joint shaft.
take all this and head down to the drive shaft shop and they make you one.
of check out tom woods web site, great info on how to fit and measure for a shaft