Some of you had ideas about influences from Italia or Germany. You were on the right way. This piece is a german concerto in three parts (Animoso, Adagio, Allegro). The composer belongs to the "Berlin School". I encourage you to listen too to the wonderful Johann Gottlieb Janitsch's triosonata recorded by Edol. Both composers were closed. This concerto is the only organ piece from Johann Gottlieb GRAUN, well known for his violin concertos. He is the brother of Carl Heinrich, famous opera composer. He learned with Pisendel in Dresde, and with Tartini in Italia. He teached to Wilhelm Friedeman Bach.
This concerto is in a well known manuscript in Brussel. This MS contains copies of CPE BACH organ sonatas.
The MS has clear indications about the use of 2 manuals and pedal.
Looking forwards on the web, I can say that I propose to CCH users a real "Première" because this piece has never been entirely recorded.