Unfortunately I've already had experience of rolling a loaded 38T log truck, (when the front left axle mount on the tri-axle trailer snapped, whilst negotiating a downhill bend in a Scottish forest) putting the trailer and my Scania 113M on its side against a cliff wall
Since that day, every wobbly trailer gives me spine shivers.
Without meaning to offend, the load is also worth more a bit more than a load of hay, to me anyway, so the boss would never let me put any risk on it.
Struggling to get insurance for it, as its not an aircraft, as it has no wings or engines and its not a vehicle, as it has no wheel!!
Trying to get a company to insure it simply as an historic display item is near impossible.
Anyway, I'm currently researching the idea of a mid 90's TDI or 130 Landrover, as they have a 4oookg towing capacity. I just need to find someone who has one and can assure me that they can actually tow 4000kg at that age
Although I haven't tried it, I have no doubt that they can tow it (I have both a '95 130" with 4 cyl turbo, and a '01 110" with 5 cyl turbo), but you'll most likely need to be be taking off in low range and shifting to high on the go. And the trip will not be quick! (The 5 cyl is much more flexible and powerful right through the rev band, being a computer controlled motor, but then it is electronic!) I have (rarely) skull-dragged dead 4WDs through deserts (deep, dry sand with steep sandhills) using both my Landy's, and it is hard work with a small engine, esp when the traction to the ground is tricky.