Hi Doug,
I doubt that I have greater understanding of antennas than you do, but I'll give your question a shot. Actually, I have been working on circularly polarizing the ARROWS with the WRAPS lately, a work still in progress but almost complete. So I am throwing out the draft information I have been working on to date.
You can circularly polarize a pair of ARROWs and they actually work well together from my experience (one of the reasons I suspect is that the feed system of the individual antennas is very well matched). If you are mounting the two antennas virtually on the same boom (sticking them right next to each other) it might get pretty crowded and interactions complicated. I have mounted two ARROWs separated horizontally about 3 feet apart with pretty good success. I have done this with stock ARROWs, and also with one side with the two meter elements, and the other side with the 70 CM elements (had to drill extra holes for the 70 CM mod), both ways worked about the same. The tricky part is coming up with the right feed lines (the transformer lines and the phasing line).
I have a first draft of an article I am working on that describes my latest effort to come up with a polarity switching arrangement for ARROWs with the WRAPS, it can be downloaded here (if you have download issues, let me know and I'll try and get it to you another way).
Click here to view Circling the WRAPS https://www.dropbox.com/l/xvKKUtfwUN5gFhGyCiXjua?
I will be adding to the conclusion of the piece some suggestions on where to include an external diplexer in the line to handle the single feed line issue that you mention in your post.
Anyway, I hope this will stimulate some ideas.
Mark
Mark Spencer, WA8SME
860-381-5335