I have rebuilt many and many of those. With the quaiffe internals, you just need to improve oil ways and distribution and be very accurate in the settings of the pre loads of bearings. Beside this, it is a very good gearbox for the price.
One thing to check, if you do not have a quaiffe LSD, is that at least this gearbox went upgraded with a four spiders differential. 2 spiders, standard UN1 are weak and put your gearbox at risk. Four spiders diff can be find on lotus, Alpine and the truck version of the UN1 (UN5) where a lot of internals can be swaped with UN1 including the four spider diff.
Best