I also have 68-72 340 and 68-72 318 k members There is a difference between the two. 340's have extra bracing at the lower control arm area. Actually all a-bodies with a factory stabilizer bars have the extra bracing welded on. This can be easily duplicated on all.
A way to easily tell is by looking for the washer welded on the front. If it has the washer it came with a stabilizer.
$175 shipped for a 340. cleaned and ready to install.