Well, you'd want to change out the LT230 transfer case for the other ratio. I get the numbers confused. There's a 1.2 and a 1.4. You'll want the one that didn't come with your Defender.
Aside being too slow, the acceleration is an exercise in patience. And hills are not to be taken lightly.
I have a 2.5L. My strategy is changing. The goal is not to stop ... ever. I find that accelerating from a stop is a lot slower than if I'm moving. Being able to foresee instances where I can slow down sooner to maintain a continuous forward motion is a skill I'm slowly learning.
If you're serious about diesel, you'll do better with a newer engine. At least the 2.5L if not one of the later turbo charged engines. The 200, 300 or 2.8 are good alternatives. Cost goes in that order, too (2.5L, 200, 300 and 2.8).