Except for the 1967-'69 427SS the words SS means bucket seats, not suspension or motor upgrades. SS only buys you chrome trim not performance. As such look to the station wagon or Police car suspension parts if you want to upgrade to a heavier duty than stock.
The F-40 option after 1969 when ordered with a new Impala bought you HD suspension: consisting of a stiffer spring rate stiffer valved shocks and sway bars comparable to what was included on police cars before that time. On a Chevelle SS or a Camaro SS (includes same parts as used on the Nova SS) the suspension upgrade that was part of the SS package was listed as F-41. However you could still add to it by ordering the F-40 HD suspension upgrade on top of the F-41 to double down on the suspension upgrades to the point were a lot of people took them to the track with just the factory installed parts (think TransAm road racing).
There probably are not a lot of early sixties police cars left in bone yard but I would consider looking for one if you want to upgrade your suspension parts. You can of course buy new springs wound out of the same size wire as used back then for police work, it is just a matter of looking in the catalogs. It would be much easier however to talk to a sales engineer at Eaton or Moog to talk with him about your desired handling goals and ride height. You can also buy today better shocks than were offered back in the day. The aftermarket offers sway bars that are bigger and better than the factory originals as well. Check out Hotchkiss or Affco catalogs to see what is available.
Keep in mind your car today is sitting an inch and half to two inches lower now than it did when new (Spring Sag). As such keep that in mind when ordering new springs, as it will rise up at least two inches when installed if you specify stock ride height. To lower it more than what you have now you would choose a lowering spring (generally two inches lower) and add to that a two inch lowering steering knuckle (where the spindle height is raised two inches higher on the steering knuckle to lower the car two inches).
The sales engineer is going to want to know what your car weight is so it has to be measured using a truck scale (accurate to twenty pounds) or trying to get the true four corner weight using portable scales. Your friendly DOT police officer has a set of scales in his trunk if you can bribe him with donuts and coffee at four in the morning to set them up for you in the parking lot of the closest chicken coup to your house. Also if you live in the south there will be in some industrial warehouse in your town a Roundy-round racer that has a set of four corner scales that might help you. Best way to find them is to cruise the warehouse districts in the evening as they work after hours on their circle track race car replacing sheet metal and freshening or adjusting the power train and suspension for there next demolishing derby.