SS was not a performance option. It, the SS, could be purchased with a six cylinder engine and a PowereGlide, with the standard marshmallow soft suspension as any other full size car.
Sorry to get off topic with the following info; though it still applies to you. But I thought for some reason that you had a 1967 Impala. Chalk it up to short term memory loss.
There were only three high performance full size cars made in the years 1967, '68 and '69 time frame. They were all based upon a Cop Car (9C1), with the standard high mileage 350/305 SBC engine pulled to be replaced with a 425 horse 427 BBC engine.
Then the spartan (rubber floor mats, no radio interior) was completely redone with SS trim (loop pile carpets, buck seats, AM/FM radio, and all the rest of the chrome bling). In addition to horsepower, the 427SS Impala came with heavy duty cop car suspension (think of the list of options from the Blues Bros. movie), power disc brakes a TH400 transmission or a Muncie four speed and a 12 bolt rear running 3.55 or higher rear gears, HD cooling and HD charging circuits. The SS427 had one other thing that none of the other full size cars got. A one off hood with one or two blisters with a chromed fake air grill on it: that if you could find one, sells for over $6,000 on flea-Bay now a days.
If you want a performance package find an old cop car that has a "certified" speedometer that goes above 85 mph. That will be a 9C1 cop car (and it will probably be a smashed wreck, as that was the fate of most true cop cars). That potential parts car will have HD, suspension (RPO code F40), Heavy duty Cooling (a bigger radiator, has a cooler for the power steering pump, and a separate cooler for the transmission in front of the radiator, in addition to the one in the radiator that most cars have), big SI 12 78 Amp or larger alternator, 780 Amp hour battery, HD starter motor, TH400 transmission, 12 bolt with a 3.23 open rear end (cop cars never have positraction because it causes the car to spin when you have one tire on the pavement and the other on grass as you try and pull back out into traffic after writing a ticket). bigger than stock sway bars front and rear and stiffer than stock springs with super duty shock absorbers. A Cop car is as heavy duty as you can get it, ready to race, or prowl dark streets full of pot holes.
Most had a HO (high out put) 305 or a standard 210 horse four barrel 350, and Z rated factory tires (today's P235R15 cop tires are rated W) that allows the factory to install a high speed module in the car; as it is the tires mounted at the factory that determines the car's top speed, not the engine. Even a punny 305 has enough power to push the cop car to 148 mph if you give it a five mile run at it to get up to speed.
Here is a true documented 1967 SS427:
Note the hood blister in picture #7. Look at the three videos on Google of people trying to sell a fake aka "tribute" car without the hood blister. You can buy the SS427 trim piece for $30 bucks, but without that $6,000 hood no one will believe it. By the way there are more '67 model year SS427 Impalas than any other year because in 1967 Chevy introduced the Camaro with a 396 that ate the heavier SS427's shorts.