Bought two new taillight lens and bezels.

They appear to be exactly the same in depth and thickness to the factory parts but the factory screws that go through the bezel then the lens do not engage the bucket - any idea what gives?

Looks like there should be longer screws but this is a factory built car that no one has messed with.

the screws that you have are most likely for the 1971 Road Runner which uses the same tail light lens but without the bezel. the thickness of the bezel is your difference. the 71 GTX screws are slightly longer . Cant tell you the exact length ,it was a long time ago , but you might try getting in touch with 71GTX he may have some laying around.