Even if you knew the STC requirements of the 70s, your question assumes that everything was built to code when your place was contructed. Since you can't really know that for sure, you can only conduct tests from the adjoining units. If that's not an option (and it probably isn't), you're going to have to look into how you can ensure that your walls meet a specific STC rating. This means that you will need to research various soundproofing options, the most popular of which are 1) floating a wall on RSI clips, 2) soundproofing compounds like Green Glue, or 3) specially-designed acoustical drywall like QuietRock. There's also MLV (mass-loaded vinyl), but the material and shipping costs of that are outrageous which renders the return investment in soundproofing quality pretty minimal. You also need to know that low-frequency sounds are very costly to dampen and that the STC rating system is pretty much designed for frequencies at or above 125 hz (I'd like someone to correct me on this one if I am wrong).
As bcworkz also pointed out, you need to consider flanking paths like ceiling and floor, especially if you're in a multi-floor, townhouse-style unit. If the room you're soundproofing is on the top floor, you need to consider your flooring since the sound waves can travel diagonally through your floor and right into the first-floor living area of your neighbor's unit. They can also flank which means they vibrate your subfloor which vibrates the joists beneath which will end up vibrating your neighbors joists and then your neighbor's floor. Also consider attic space above your room which can serve as a potential top-level flanking path for sound much like your floor.
One of your best bets is to introduce yourself to your neighbors. Let them know that you are conscious of your noise production and that you want them to alert you of any disturbing noise entering their unit that originates from yours. They will most likely deeply appreciate this gesture and gladly comply. This means that you will have a good chance in knowing whether or not your noise requires dampening and, if so, to what degree (see aformentioned paragraph about soundproofing options).
In the end, you're going to be left with taking a stab in the dark. Even if you read on some website about how adding an extra layer of drywall with Green Glue in between will give your wall an STC of 56, there could be a good number of other unaccountable factors can totally throw of your initial STC calculations. This can result in lower-than-expected results and will require additional soundproofing application on top of what you've already done. Expect to spend several thousands of dollars to get a satisfactory result.