Solos are in the trumpet 4 (with electronic delay) and alto 2. The trumpet soloist’s delay can also happen from the sound board in performance if you don’t have trumpet electronics available. But you should make sure the soloist hears the delay in the monitor.
The doubles in this are very minimal, so minimal that the clarinet parts could maybe be played on alto if necessary. And, while I enjoy accordion on this piece, if you cannot find one, is not a deal killer in playing this piece, but you will miss it somewhat, especially on the ending. The score is written for: 5 reeds, 4 trumpets, 3 trombones (lead needs harmon), 1 bass trombone, accordion, guitar (electronics essential), piano, bass, and drums.