It looks like your setup would work well.

I am curious about one thing:

By "forward crossbeam" you mean a third crossbeam in front of the main (mast) crossbeam, am I correct?

If this is the case, then your setup is better then the usual spinaker pole setup because chances are that a forward crossbeam is not designed to support the additional load in the middle.

If you don't want a forestay to keep the tip up, maybe you could use rigid bridles (carbon would be best but wood or aluminum are fine too). Just raise the tip enough to avoid that the bridles are in the same plane as the former masts and it will stay in place.

Cheers,