as stated above just buy a cheap 3.9 ratio r160. then take the r/p out of it and put it into your lsd r160. that way you have lsd in the rear. my friend had a open 3.90 r160 and we went through three of them in two months. open diffs in the rear like to break spider gears quickly! he was on a 30r on the ej205. we did three launches on one and it was gone. only lasted 20 minutes. thank god the local scrap yard gave us a one year warranty on it. and when they ran out of them they gave him a full refund lol. now its a 3.90 r160 with a 3.54 r160lsd.
a auto wrx driveshaft might be hard to find but is needed because of the different length.