I am in the same situation. I had springs delivered. I will replace gas shocks too. It will even out the ride. CDNPONT, A member here mention air-ride. A bag that goes inside the coils springs. That seems to be the answer. Around $100 per coil for the air bag. Let us know how you decide, and the outcome. Tks

Install BIG BLOCK station wagon springs and gas shocks. Guaranteed to solve your problem. Will ride a little stiff at the begining but WILL mellow out .

Yes, there was a time back in the 80's when most part stores personnel still knew and understood what a Canadian Pontiac was.  Sadly, those days are long gone now.  Recent trips to Crappy Tire and Parts Source have confirmed that when you ask for parts for a 70 Pontiac, all their systems bring up now are the American models.  Therefore, if you are looking for anything mechanical, just tell them you have a 70 Impala and be done with it because from a chassis and drivetrain perspective, they are the same.  I tried to explain to the 20 year old kid at Parts Source what a Canadian Pontiac was and what the differences are with American Pontiacs but his eyes just glazed over...