Sadly there are very very few tyres that are rated to carry over 1750kg EACH unless you go up to 17.5". I only found 1x 16" tyre that is UK legal and that is like £350 for just one! In 17.5" size there are loads available.
Haha, Yes it will almost fall on and almost certainly fall off. The size refers to the diameter at the bead so it won't seal with a 1/4" gap all round.
Well you could poss run/weld a 6mm strip round the inside of the wheel bead if done correctly it should work depends on the size of the vertical edge rim. They are slightly varying sizes in fact the tyre would never come off when blown anyway because of the steel edge bead in the tyre.
Yes the axle is 3500kg. Seriously heavy duty. Originally there was a compressor on it which they took off and mounted on a lorry which was then shipped to South Africa to a mine. I suspect the axle and T bar weight about 500 or 600kg so the compressor would have weighed about 1600kg which is just within the capacity of the current tyres.