Surely the ScanSpeak mentioned is the replacement for the later midrange unit with the black dome? The picture above is the earlier unit with the clear dome, which is not the same.
As an aside, is the ScanSpeak an exact replacement for the later unit? I’m tempted if so as I have another noisy midrange driver on my MS150.2s.
To the OP – for glue I would just use standard PVA. It allows for easy positioning and will hold the dome in place fine when it sets.