New to Subaru, so bare with me.

Im buying my buddys wifes 99 2.5 RS coupe. Shes an idiot who ran it till it blew up and now needs a new motor. I have a line on an STi motor and tranny, but not sure if the tranny will fit in the RS. Anyone know if it will fit or what needs to be changed so that it will?

It will fit, you'll need to know what year the trans is from in order to get a matching rear diff ratio. If you use an sti diff (r180) you'll have to change rear subframe, axles, and knuckles to match. You can use a regular subaru rear diff (r160) and axles with the correct gear ratio. And mate it to the 6 speed using an automatic impreza driveshaft. Do some research on rs25.com, plenty of information specific to that car on that site.

Thank you!!

Ill probably go with the the second option since it is an auto, and also sounds like the cheaper option. Cant find the interior parts for when I change it to a manual though.  

Interior parts can come from a 98-02 forester as well.