This is going to sound both silly and insulting, so please be assured that I don't mean to be, but A) I've just watched your video of it dying, and B) I've just read the whole thread, and I don't see any mention of...
Air starvation.
Now before you scoff, just think: if air was being restricted flowing in through the bodywork grille and ducting into the main fan, then the air supply to the outside of the engine would be too low, hence the overheating, and the air supply to the air filter and hence to the inside of the engine would be too low, hence the cutting out, and the excess of petrol over air leading to the 'too rich' smell.
It's only a theory, but like I say, I don't see any mention of a new air filter, or checking the air ways. Easy test: run the engine as normal (so as to get as much cooling as possible) until it is starting to cut out, then whip off the air filter housing and air filter, or at least disconnect them so that fresh air can get into the inlet without restriction. If my theory is right, the engine should pick up again (but don't let it run too long on unfiltered air and without the full cooling flow).
If my theory is wrong, then the engine will just cut out completely as before.
And now you'll tell me oh yes, we did fit a new filter but forgot to mention it !

Anyway, really hope it's some blockage in the airway and not a cracked cylinder head

Good luck