I have been told I need a new short block in my Kia Picanto. Yesterday a man from a breakers yard recommended that I change the whole engine rather than part of it as in the long run it is less complicated.

If I do choose to replace the whole engine with one from a similar but newer car that has less miles on the clock are there laws governing this? For example the new engine will have a different number, does this have to be registered somewhere? How many miles should it show in my car - what the car has done or what the engine has done?