[why]

Want something different than 4.0, do I have any options?

 

[redtruck12]

You have lots of options .... None are going to be cheap though.
Diesel conversions are available but from what I have heard "not very peppy"
Lots of discussions of small block Chevy conversions but lots of complications.
What do you want to improve? Power? Reliability?

 

[MykD]

Got a buddy in South Louisiana that is running a 300tdi in his Disco 1 with a 5 speed transmission! It's a beast.

 

[number9]

Want something different than 4.0, do I have any options?

How about more info.

Do you currently own the vehicle/how long? Why not wanting 4.0 when there is so much to love about it?

......