If it still has magnetic pull, glue it and try it out.
What ever will keep it from falling apart when you install it in the pickup. I've used super glue on things like this since it's just to hold it in place.
I'd suggest wax potting it to prevent microphonics.
what's the difference between the alnicos in sound ?
You would wax pot a open coil the same way as you would one with a cover.
The only reason I suggest it is if you're using high gain and you're worried the 2 magnet sections might rattle against each other.