I happened to notice a metal plate rivet to the passenger side door
frame (right side). The words are in german and I'm too lazy to
babelfish them...

There are 4 sets of numbers.

2500 kg
4500 kg
1300 kg
1360 kg.

I'm going to presume that the first number is equivalent to the GVWR
(i.e. total weight of the Tristar and its contents). And the last two
are the maximum load on the front wheels and the rear wheels (in that
order.) it's that 2nd number that puzzles me.

4500 kg is over 9000 lbs. This must be, I guess, the maximum towing
capacity (presumably with brakes on the trailer.)

Any body out there that can confirm my suppositions?