Rex Basterfield makes tons of free synthesised VST instruments, but created an interesting 'resonating sound box' effect earlier this year that would seem relevant here for the box tone:
https://www.youtube.com/watch?v=5NBm0CdJ8x0
Got to recommend his Sim-Cimbalom instrument too... he created and released this amazing synth 12 days after I suggested it!
https://www.youtube.com/watch?v=ALKOXqQXyTs
Many of his instruments provide little details along the lines of those in the article (see his narrated YouTube vids), all freely-available here, most-recent at the bottom: