Hans Keller suggests that this version of the Adagio and Fugue isn't as authentic as it looks, while the string quintet arrangement of the Clarinet Quintet seems, on musical grounds, Mozart's own.
ALLEGRI STRING QUARTET with CECIL ARONOWITZ (viola) Part 1
Busoni String Quartet In D minor, Op 26
Mozart Adagio and Fugue in C minor (K 546) (for string quartet)