Originally Posted by fusionchicken
just like the above poster said, just slide the tranny right into your existing axles. for me i had to buy stubs and circlips to make my 2005 STi 6spd (also a female end) fit onto my front axles. 2004 6spd has stubs already sticking outta it.
for your driveshaft if it fits between the 6spd and 3.90 R160 it's most likely customized, or off of an automatic subaru. for example i'm running an automatic Forrester driveshaft on mine - 05 6spd mated to a 3.90 R160.
if you want to use STi axles you need to get STi hubs/brakes/etc., or you could modify the end points of the axle to fit your WRX hubs. but your main issue is i dont think the STi axles would fit on the R160, and I'm also not sure if your current WRX axles would fit on the R160, but if it would then everything will bolt right on - just reuse your axles/hubs/brakes etc
the sti axles will not fit in the rear due to the r180. and your wrx axles would not work on the r180 ( i think that is what you were trying to say above). you can use sti axles up front as long as they are from an 04' sti because of the outside connection with the hub is the same, unlike 05-08 sti's. DSS used to make conversion axles for the r180 to be used with their axles on a wrx, but they were discontinued.