tiv

Could be better if you can specify which year and transmission etc
A 4m41 off a montero will span about 800k LKR and go upto 1 Mil based on bits included
4m41 has a bit more grunt but also a troublesome engine, sometimes a proper OCD level rebuild of a 4m40 might be worth it in comparison to a 4m41 from a half cut car.
Of course you get to brag about the 3200cc but in reality even a 2500cc 4d56U turbo can make that power in their newer guises in newer models.
Of course it can be done and there are people, depending on your locality.
My knowledge is a bit dated on DMT matters but AFAIK there is a CC limit you can go in an engine upgrade. So check with them or else your vehicle wont be road legal, and given the times selling will also be a nightmare given the CR is not updated 

Is this a front tyre or rear tyre? 

It's not that difficult, a skilled mechanic can simply mount them, just 3 points 
You 'll have to resort to used seat belts off car parts shops or else pay premium to get sets off agents. 
Matter of fabrication of brackets thereafter. Depending on what your vehicle is

Looks like they've spent more money on fixing up the book via DMT rather than on the vehicle lol. ?
 
Even a noob about land rovers would know the defender name was not even introduced in the 80s. Would have looked legit if they fixed it to be land rover 90 or 110 which they were badged as at the time and that was how the bookes were printed. But this series 3 should have been just land rover for make and a "-" for model. Some genius decided to fill the gap and alter the book.
STF vehicles bearing reg nos 32-23xx just had the tag Land rover but they were real 90 soft tops those were the first 90s that came in to the island With YOM 1985. Some are still in service. The First 110 was released in 1984, first 90 in 1985
Even defenders from 1992 don't have books bearing the name DEFENDER, just Land rover 110 or 90.
If the book is your target. You can't use this reg on a defender on a legit basis . A known cop will take you in as its a 31 Sri. Mind you cops know about these vehicles as most were ex police army etc. Unless u change it to a E series number but still there are many holes you can get trapped into the law with this. Given all the spending and the condition the thing is in. You might be able to buy a real defender 90 or a much more reliable pajero. Mitsubishi jeep etc. For that money. Or a properly done up puma or near for around 6mil.
If you think owning a defender and hooting about can kinda give you that macho political big shot aura in town. Sadly that era has passed and now they get copped in and out. No one cares. Believe me I owned a legit one few years ago in army green and had a past time of living with mechanics and paying cop fines.
 

Try early pajero SWB or 4DR6-T
Based Safari body Jeep units

Your question is not clear, If you are talking about the Auto function, usually disconnecting/reconnecting the battery works. Or there will be a specific sequence to reset the system, This is usually present in the service manual for your car.
For example something like this in my vehicle