Hi ,
looking for advice again .
I have a early Defender TD5 with engine probs , and the chance to buy a similar aged discovery with good engine but failed M O T (dont know why as have not seen it yet) question is how easily will engine swap from Disco to Defander ? thanks .

Straight swap !

You might need "nanocom" to sort a few bit's of electrickery out !

As Jason says straight swap.
There are a few plumbing differences between the early 10p engines and the later 15p engines but nothing too difficult to sort.

If both engines are the same number series then you could swap the injectors, making sure you put them back in the same cylinder positions and you would not have to code the injectors to the ECU. You can not swap injectors between 10p and 15p engines.

If the Disco engine is a good one then go for it. Just check for the dreaded diesel in the sump oil before committing. It would also be worth locktighting the oil pump sprocket bolt on the replacement engine before you fit it.

Many thanks for your help guys . J

Done this and yeah it's straight forward swap the injectors as per cylinder but if so make sure you fit new o rings and washers then set the injector bottom outs (bit like setting tappets) when rocker is pushing an injector down undo nut and wind in then back off 1 full turn
Just be sure to put car into bleed mode to purge fuel system
So long as both engines are same type with egr or cooled egr types then you'll be fine