From what I can gather based on a quick look through various PDF owner's manuals/documents from my M-Tron Pro folders, here are the matching M400 sounds as identified by GForce:
Stock M-Tron Pro soundbanks:
Choir 1 - M400 male choir
Choir 2 - M400 female choir
Choir 3 - M400 boy's choir
Synth Trumpet - could be ARP or Moog, taken from an early M400
Streetly Tapes, Vol 1 Expansion:
M400 Violins
Streetly Tapes, Vol 2 Expansion:
M400 Vibes
I don't see anything that specifically identifies "M400 Flutes", but it's likely they just re-used the same flute sounds from earlier Mellotron models. I think the original Mellotron flutes actually came from the Chamberlin anyway. There are several flute variations within the stock M-Tron Pro soundbanks, as well as in the Chambertron Expansion.