Indeed they do. I have a little 30 year old sports car and the related owners forums have entire sections devoted to modifications to boost the original engine or to replace the original 4 cylinder with a 6 or 8 cylinder engine or a rotary engine or an EV drivetrain or in a few cases to fit a smaller and very frugal engine. And another entire section devoted to fitting this 1990s car's drivetrain into trackday kit cars or retro-cool older cars.
I also sometimes read build project threads about entirely unrelated models of car too, yet I have never ever seen anyone convert any model of car into a diesel hybrid.
The thing you discover is that, even if you do most of the work yourself, doing it right gets really expensive. So people do not buy a hobby car to modify it into another available model of the same car which they could just have bought ready-made anyway.
TL;DR The reason you can't find an example of anyone converting a diesel Range Rover into the diesel hybrid version is because nobody has done that because it's pointless.
There are youtube videos which explain how cheap and easy it can be to convert an ICE car to hybrid or EV.
https://www.youtube.com/watch?v=dXCTXxL5lr0
How CHEAPLY Can You EV Convert Your Old Car?
https://www.youtube.com/watch?v=ZYbMuHpa6wY
Simplest EV Conversion under $3000 - Convert Your Car in 3 Days!
I looked on Google and a replacement battery for a hybrid costs between US$2,000 and US$10,000.
So when my car was written off by my insurers due to the cost of repair exceeding the threshold of circa three-quarters of its market value, despite my pleading with them to pass it for repair*, it was bought by a typical salvager, such as Co-Part and sold on to someone. He contacted me and requested the second key and defa heat-lamp cable (I had tried to send the key to the initial salvagers with no luck and it being returned uncollected). Now this cable is only worth about €20 in a local hardware store and it connects an engine block to the coolant to stop it freezing in wintry weather plus for inside heating to stop the car frosting up overnight with snow and ice, so I presumed he was planning to fix it and resell it.
With the hybrid battery alone, it might have been considered worth his while buying the car on auction for a few hundred euros, probably more as it was less than three years old and only had about 5,000 kms on the odometer.
The initial garage for the insurance company had said it was too expensive to fix because the floor was bent and the wheel axle damaged, together with the wing mirror broken and the bodywork dented. The back of the car was untouched. The selling price is hidden although I could see the car sold on their webpage.
So, all a car enthusiast needs to modify a diesel into a hybrid is the hybrid battery and some mechanical know how. Plus, of course, you need the relevant permissions and approval from DVLA to reregister it.
*The sorrow turned to gladness when I was reimbursed what I had paid for it, as here, if the car is less than three years old you get the market value, instead of a heavily depreciated one. On the downside, the price of a new model had gone up quite a bit so I had to use some of my savings to make up the price difference (but at least it won't need an MOT for four years).
I went up the motorway to call the emergency services from the nearest phone on the hard shoulder (students def couldn't afford mobile phones in those days) and a fire engine had reached my car and drenched it by the time I returned to the vehicle. Needless to say, it was a write-off, and a slightly scary experience.
You must have a very very very low opinion of the police and fire depts.
