Will the Koala rings suit the Cooper Tunnel?
Yes.
Will plastic rings fit?
Yes, provided they have a cutout to locate on the lug in the Cooper Tunnel.
Would an adapter be required to fit an Eagle-Eye?
No. Whether using sights for rings or variables, both Precision Sights are compatible with an Eagle-Eye.
I have been using a Koala. Will the dove tail on the Precision Sight fit my rifle mount?
Yes.