I have a 1970’s fluorescent single bulb fixture in my kitchen. It has no markings. I need to replace the tombstone. The fixture is part of a group of fixtures along the wall/ceiling joint around the room with plastic lenses — I believe it was called cove lighting. Over the years I have changed ballasts and tombstones on several of the fixtures. This 4 foot fixture is different. I cannot remove the cover to access the wiring, tombstone or ballast. It has nothing to release the cover and I can’t pry it off — I can feel something holding it in place. Other than two dimples on the side of the fixture case 18 inches from the ends, there is nothing. Does anyone know the cover release trick? It is a heavy old school fixture not the modern lightweight cover you pinch and release. Thanks.