Looking for information on putting a 1996 Disco engine and 5 speed transmission into my 2000 Disco. Any information will be helpful.

 

It won't be legal. A donor engine has to be the same year or newer than the vehicle it's going into. And the engine management on the 2000 is Bosch instead of GEMS on the 96. Bosch is a whole lot better.

 

Past not legal, it won't work. Your current ECU has to see a ZF tranny or it won't run and installing a 96 ECU won't cut it either.
As AK mentioned, you can only upgrade on engine replacement not down grade.
It would cost you a fortune but you could go thru the UK, buy the proper UK ECU for a 4.0 engine and a 5 speed, then modify to adapt the 5 speed, it will cost you more then the truck is worth.
That being said, why would you want a 5 sp in a D2?

 

If you're interested, a bloke on Discoweb.org has converted his DII to an Isuzu diesel and manual gearbox and loves it. So something like what you want is certainly doable.