The suspensions are identical, except for the bushings on the lower control arms. There is no way to tell the difference, except to measure the outside diameter of the inner sleeve in the bushing. The early (pre-1972) bushings had a thinner wall (same inner diameter), so the rubber part of the bushing is thinner. The old inner sleeve is 0.710 inches in diameter, while the later sleeve is 0.745 inches in diameter. The thinner rubber made a less "compliant" (less flexible) lower control arm, so it wasn't as prone to highway speed shimmy (the key word is "as prone"). But to measure it, you have to tear the bushing apart, since the factory bushing uses a rubber core that is "vulcanized" (adhered) to the inner and outer sleeves.
Where this matters is if you replace the old rubber bushing with a polyurethane bushing. Which, by all accounts, is a good thing. When you do this, you usually still use the old inner and outer sleeve of the stock rubber bushing (you burn the rubber out), so you need to get the correct poly bushing to fit whatever inner sleeve diameter you have. Or you can order a set of new-style inner sleeves from OGTS (#3059, $49.20 per set including the upper control arm bushing sleeves) and replace the old inner sleeves with the newer, thicker version. The poly bushings will rotate more easily on a nice new clean sleeve than an old rusty one.
There is an earlier thread which has some useful information on how to change over to polyurethane bushings in this forum. Just do a search and look for "sleeve" and "polyurethane" and "control arm".
HTH
