um depending on what size turbo you want along with how much you want to spend and how long you want the rest of the engine to last is up to you, but a simple 1 would be a standard t2 hybrid rollerbearing with mods to the housing, then u can go t25 hybrid, t28 hybrid, t3hybrid, but the higher you go the more lag u get, etc, if you go bigger, you really need to look at putting a stronger headgasket on etc, and making sure your intercooler will stay in 1 piece and not explode, i had a r 5gtt standard intercooler on my 440 the other week seeing if it made much diff to the 1 i already had, and i blew it to sh*t running 15psi through it,
there are lots of things to take in to account, but it is a pretty much simple unbolt and dissconnect oil pipes etc, and bolt on new 1.