Sounds great as is. An upright bass and jazz drums
would sound great with this too. or
Classical guitar
Acoustic guitar
sax
Brass section Think of "blood sweat and tears")
female voc background fills
upright bass without drums.
Any one or combination of the above is about all I
can think of if your looking for thoughts on instrumentation.
It carries itself well as is too so either way its a great piece.