All 70s have screws. Early 71s have screws and late 71s have the clip in type.

It's possible no numbers on the rad core support, but I would look again where the top of the radiator corner mounts closest to the drivers side, where the yellow rad sticker usually is. Hard to see with the rad mounted because it is usually not stamped on the top rather facing the rad. Sand off the paint in this area if you want to be sure. Hamtramck cars as well as LA e bodies are similar:)