Its sounding good. A nice feel and atmosphere. With some different vocals it will really improve things, it still sounds really good with the originals. As far as the structure goes, I do feel that some fat could be trimmed. The song flows beautifully but the instrumental break at 2:28 I'm not sure of. The sax solo later makes it feel a bit redundant but i don't know....I'm unsure of it. With it being a song/vocal track it feels a little unbalanced (structurally) with the breaks. The end section from around 5:00 mins could do with more interest and/or shortening. I'm sure that you will be developing this section anyway as it is a WIP but it feels to me like there needs to be either a key change or a more prominent/energetic counter melody to the lead.
Having said all of that, though, the fusion of all the different sources is really well done. Perhaps its not so much that the earlier instrumental sections need to be trimmed, I understand that they are from different sources, but perhaps if interjected later could counter the last section from 5:00 onwards and give more interest.
All in all, I really like it and it is clearly going to be an epic when finished. What I will say is, that despire my above comments, if you're happy with the structure keep it as it is