Removing 2.8 trooper out of my defender 90 and replacing with 300tdi

Hi all, hoping to get a bit of advice.
I've got a 1990 H-Reg Defender 90 that I bought with a 2.8 Isuzu trooper engine (4JB1T) fitted in it by one of its previous owners.
It's getting a bit noisey and lazy now, so I've bought a 300tdi engine to throw in it.
I wondering what will be involved in the job if anyone can enlighten me a bit about the conversion it's already got.
Am I going to have to buy another gear box aswel to use the bell housing off it for mine ?? Surely a defender gearbox bell housing isnt going to bolt straight upto a 4JB1T engine block ??
Also, am I going to have to move my engine mounts on the chassis ? Or will the 300tdi engine drop straight onto the mounts on the chassis that the original Land Rover engine sat on ??
Hope someone can answer my questions, no doubt someone will of asked the same questions at some point !
Thanks in advance.

The trooper engine probably has an adapter plate to make it fit the original gearbox post some photo's up.

I would say that it's almost a certainty that you'll have to move your engine mounts as I'm guessing that you would have originally had a 200tdi fitted that would have different mounting position to a 300. What rad have you got fitted? Also what pipework have you got with your new engine?

As blackburn says you should still have the landy box with any luck and it you will almost certainly need new chassis mounts as 200 mounts are different and i cant see trooper mounts being any good either

Not a huge job though as you can but the mounts or cut them off an old chassis