drive shaft question

ok i was going to do the hack n tap sye and run a stock xj front shaft. i have a 4.5 rc lift. my question is: do i have to have the xj front shaft length changed. i have been told on other forums that i have to shrten it and other forum say i have to lengthen it. so now im asking the right people. any advice appreciated. and yes i know the hack n tap is not as strong as the hd short shaft sye but thats what i got to run until i have the fundage for the right setup. thanks

It depends on allot of things. What motor and trany you have. And what rig you get it out of. They are different auto or manual. And what axle you have