I believe back in the day it was recommended to silicone glue them in. If your not intending to reuse them reach in there and tear em out. Lol. or Take a dull x-acto blade and go around the glue joints and they should come right out. Now if they epoxied them in I'd just cut on either side of the formers and remove them and then dremel out whats left. Should be pretty easy however you/they built it.

Tim