If you have not yet seen the original post about my Merry Go transcription for player piano, please read about it here.
The transcription was initially organized in four voices in the Lilypond source file. This made it relatively easy to direct Lilypond to write out a couple extra scores for a single-piano duet version. The two treble voices can be played by Primo, and the two bass voices by Secondo. This shows the power of Lilypond for maintaining multiple renditions from a single source file.
The duet was still not immediately playable. A few chords had too many notes and needed minor tweaks. The last 3 measures needed an alternate playable version; I think I struck a reasonable compromise by having the players alternate the fast final runs, and by reducing the 3-octave run to 2-octave. And in this version, the final chord does not contain all eight C keys on the piano!
As of this writing, the duet has not been performed by two people. I did record myself playing Secondo and then played Primo over it, but there may remain some awkward overlaps with two players on one piano.
If you’d like to print the 6-page duet for performance, I would recommend printing page 4 as simplex, pages 1 and 5 as duplex, pages 2 and 6 as duplex, and page 3 as simplex. Then you’ll be able to have Secondo on the left facing Primo on the right, for 3 pairs of pages. The page numbering is designed with this scheme in mind.