The stock setup is not that bad the part that usually is the weak link is the pump if you swap to a saginaw pump the stock box would be fine. Like PAPITT said they will all cost about the same in the end. Even the 78/79 box which is the most common swap/upgrade all said and done will cost you close to that. As you will need 2 boxes to swap parts a seal kit then hope that its tight and setup correctly when your done not to mention that you will still need a pump, pulleys, brackets, hoses, Ujoint to connect possibley a new drag link. Once you add it all up the $500 stock setup is a good deal even if you have to upgrade the pump. Many of the kits out there are very well priced as you are getting a new or rebuilt box and the rest of the setup usually all thats lacking is pulley's.