To put a 1996 Camaro Z28 6-speed into reverse, you need to fully depress the clutch, move the shifter all the way to the left, then push it slightly forward (towards the driver) before moving it back to the gate for reverse. Think of it as a slight "double-clutch" or slightly pushing it *through* the reverse gate.
It takes a little getting used to, but it's essential to get the feel of it to prevent grinding. If you force it without properly engaging the clutch and following this motion, you could damage the transmission.