yes, that's correct on the '73 being the only 240 with factory rear sway bar mounts. however, i ordered the 280 kit for my '73 right after finding that price with summit racing. unfortunately, the rear bar 280 sway bar won't work on the '73. while technically the mounts are there, they are in the wrong location. the front inner control arm bushing bolts are right where the bar needs to be. i was hoping to use this bar since i had to remove my 240 sway bar when i converted to the z31 cv's.
i compared to my '78 and '76 280's, which the bars easily fit, and noted the difference in location of the sway bar mounts. i have heard of someone using the rear s/t 280 bar on a '74 260, though, and will be verifying that this weekend. i'll try to take some pics to show the differences in mounting locations.
these bars are huge...