I don't know who makes the SS springs for Mopar now. I bought my 3400 lb SS springs from Mancini around 2008 and they are still on my 63 working fine. I like them because the car rides very nicely on them. I guess they were the MP springs but when I bought them from Mancini they just said they were SS springs on sale as they came with the rear hangers (shackles) and bushings for a nice price. The MP springs may be junk today or could be ok as I don't know who makes them today. If I had the money and I was buying springs today for a street/strip car I would go with the Cal Tracs for sure but I did not want to spend $800 dollars when I got my SS springs for $200 dollars. It would cost $800 or more for me to buy Cal Tracs because I would definetly use their Mono springs that they recommend. And I believe they have different heights for their Mono springs. Good luck to you. Ron