you saw that mr2 LSD on ebay too didn't you? In theory buy replacing the final drive etc with the LSD unit it wouold make it an LSD but it could be a bit more complicated-i think LSD transaxle case is actually slightly bigger and the rerason for this to house the LSD(extra gears etc)
Having pulled apart a few it shouldnt be too hard to replace the LSD unit into if the space is there.But then you;ll have to look at redoing all of the synchrols again etc-in the end it would be cheaper and stronger to find an LSD box as they had the double synchro as standard