That is correct. It was not uncommon for the feather/lite cars to not have the aluminum trunk bracing.I have seen a few like this. I guess Mopar considered it optional:-D
Bumper brackets (the shock mounts, or energy absorbing units in Mother Mopar parlance) were the same as others, it was the bumper reinforcement bars that were aluminum.
I have read several places that the aluminum intake manifold, transmission case, inner hood and decklid bracing, and bumper reinforcement bars added up to a 183 pound saving over the regular production cars, and even with the lightweight components that these cars were heavier than similarly equipped 70-71 cars.