To make an open diff LSD is quite straight forward, but costs a little. The difference is the LSD has a clutch pack connected to the Side gears on each half shaft, or some other means of restricting variations in axle speed, eg viscous coupling. Some Subarus run the same diff as z's, particularly in competition, so LSD units are quite available, especially in Aus. that will take your crown wheel and fit in your housing. In Aus you had skylines and the like some of the Japanese ones run R180 LSD's as did some Silvias etc.