Best would be if you find your original engine number (Mercedes Classic Center, buy your car's data card from them).
Then, get a 0-9 number punch set off EBay, Amazon etc (I think they are 9 mm sized) and simply punch the number from the data card into the engine block.
This was presumably what the dealers should/would have done back in the day when they received replacement engines from Mercedes and why Mercedes did not just assign additional engine numbers themselves.
Another benefit of doing this is that your Honduras-based buyer will have a Pagoda with the original engine in it, truly "numbers matching".