Will the 727 trans and 229 transfer case fit in an SX/4 with the 258?
Yes. speedo cable needs minor mods to work. like reclocking your transfer case
im doing the 129 727 swap as well, all my research said to spit the t-case in half and use the back half off the 129 on the 229 hheres the link to a very informative write up on the t-case swap
http://www.n0kfb.org/homepage/amc/tech/transfer_case/swap/
That only works if you have the dual pattern tail stock. Mine was same as the NP229 so it was a wasted effort.