unwise words - buy a 2nd hand box & lob it in - it could only last 3-6mths then you have all the pain over again. u have no way of checking the box of the car, you are simply going on the sellers word
wise words..... dont even attempt to rebuild a gearbox/diff yourself
wiser words - get your existing box rebuilt properly, the diff will not fail again - also you know the work thats been done on it - peace of mind

no point doing things in halves
also, 8v boxes will also fail at some point. they usually last a bit longer as they are never stressed as much on an 8v engine compared to a 16v engine