What you are describing is the correct rear end for a 1967 Firebird, hopefully yours is a '67.

They are actually Tempest rears pulled out of the parts bins so there are control arm eyelets at the top for Tempests that are not used on the Firebird.

The factory also installed traction bars on the axles to control wheel hop with the mono springs. To over simplify, auto cars got one bar on the right, stick cars got 2. There will be corresponding floor pan reinforcement plates on the rear floor under the seats and "Riv-Nuts" installed in the rear frame rails to anchor the front bracket for the traction bars. All axles had the flanges welded to the bottom for both bars.

The rear suspension for '67 is one of those nice oddities for '67 along with vent windows.