Very cool. you WILL like them, especially in the near field like they are designed for.
Are they 8G, or 8H?
I would only consider these in a properly designed Bass reflex. Not in a 210.
And no, not rubber cement. silicone would work well but you will have to fixture the horn so it doesn't move while it sets up.
Where did you find these? Did you get the Urei crossovers as well?
Ron