interesting, indeed. i'm not saying they weren't on your parts car, but there is no way that the suspension techniques rear bar will fit on my '73 car as the bar and the mounts currently are. here is what the mounts look like on my '73:
here is what the suspension techniques 280 bar looks like:
here is what my dirty '78 280, with the stock bar still installed, looks like (my '76 is the same):
i'll look at my friend's '74 260 this weekend. i took pics of the '73 and the '78 cars while laying next to the passenger side rear wheel of each car. you can easily see that the mount of the 240 is in a different location, further to the rear of the car. it's even oriented in a different direction.
the only way it would fit on my '73, such that it will clear the control arm bushing bolts, is either:
if it were shaped like this crude ms paint edit suggests...
or by relocating the mounts to be where they sit on the later cars.