On my way to quire yesterday I popped into the British Library to have a look at the Surry Chapel Music and Dixon's Trumpet is quite a big set-piece , occupying pages 43-52 in both the editions I looked at ( Benjamin Jacob's original of ?1797 and the 3 volume edition printed by his successor D Heward in 1835).
Not knowing that Ros has already got a version, I have had a go at transcribing the first 3 voice section (Andante affetuoso !) and the first chorus (Allegro Moderato) (with trumpet) and for want of anywhere better I have put the pdf and midi at
http://www.cpdl.org/wiki/images/3/3a/Trumpet.pdf (437 kb, 5 pages)
http://www.cpdl.org/wiki/images/3/33/Trumpet.midDoes it match your manuscript ?
I too would welcome a copy of Ros's version !