Rachmainoff → Tchaikovsky
Britten → Lerner/Loewe
Haydn → Rodgers/Hammerstein
Tchaikovsky → Mendelssohn
I'll probably want to create a YouTube version at some point [UPDATE: done!] that will reveal where all the splices happen, but for now you're on your own...which is kind of the point.
UPDATE: And here it is:
* A case might be made that the Sinfonia Concertante for violin and viola is Mozart's greatest violin concerto - and, no, that's not a viola joke.
** For the record, my lovely violinist daughter has taken a great interest in this project (whereas she usually thinks I've lost my mind when I'm using up good computer time mangling music). At this point, she's only studied the G Major concerto, but she's genuinely interested in playing a performing version of my little monster. Having kids is the best!
P.S. Obviously, this kind of project could be tried out on all sorts of genres - Mozart piano concerti, Vivaldi violin concerti, Beethoven symphonies, Schoenberg piano pieces, etc. But, I think there's something particularly satisfying about this little set. Three is a nice, manageable number, and as I've said above, these pieces really do live almost interchangeably in the violin world. So there's something natural about exploring ways in which they're connected.