John,
Yes, I did recall that Gerald Best wrote that coffee beans paid for the locomotives. I don't know where the coffee beans were grown. I have not heard of United Fruit being in the coffee business; but, could be wrong.
When I read that in the 1930s Hazi Germany had restrictions on hard money leaving the country, the "light came on" as to the reason for Gerald Best's comment.
So some one had Riechsmarks from the sale of coffee beans to German concerns and had to find someway to get the value out of Germany. So United Fruit may have traded, non-German firm to non-German firm, US Dollars or British Pounds or some other money for the Riechsmarks in Germany and then paid Krupp to build copies from BLW plans.
Brian Norden