‘68 Polara. Not sure that the spring is the issue. Here’s a picture of mine before I tore it apart in 2015. I most likely replaced these in the mid 80’s and put more than 20,000 miles on them before I parked it in ‘89. 3+ trips between Montana and Colorado in that time frame as well. Long spring on both. Replaced them with a another long spring during th rebuild and have close to 2,000 miles this summer with no issues.
Before rebuild
Before rebuild