Eaton Detroit Spring is a good bet to get it right. MC1543's. Parisienne isn't listed, but 65 Impala Convertible is certainly comparable.
Although rear springs are easier to source and get right than fronts, it still can be a crapshoot to match numbers these days. I've been down that road.
I don't trust generic part house numbers for springs. And I don't believe they tell the truth half the time. Thats just an opinion mind you.
Regardless, Here's a good link to Moog Springs for your research;
cdnpont has a great suggestion. Moog springs should work very well for your '65 Parisienne. About 4 years ago, I went looking for rear coils for my '64 CS. I tried a set of Moog springs for a '64 passenger car but found that my car still sat too level, or, perhaps too low on the back end. I ended up installing a set of Moog springs for a '64 Pontiac Safari. The difference was incredible. The Safari springs raised the back end just the right amount for my liking. Of course, I realize that everyone has his/her own opinion as to how a car should sit. If you wish the back end to sit up, you could consider springs from a wagon. I offer this as a suggestion only. Good luck.
For rear springs it's always better to buy on the side of too tall since cutting (with a standard cutting disc) is easy and in and out testing is much easier than in front. Generally speaking our cars sat with the back of the rocker a half inch lower to the ground than the front with a full tank of gas and no passengers.
This was both for aesthetics and braking issues.
I like the stock look, some people like a bit of the rake, to each his own.
