Orange Blossom Special is a three part tune, usually played in the key of E, with the second section modulating to the key of A, staying in A for the third section then returning to E.

I play this on harmonica by playing the first section cross harp style on an A harp (key of E), then swithching to cross harp on a D harp (key of A) for the second section, then, switching to first position on the A harp for the third and final section in the key of A.

This will definitely take some practice, but it's worth it.