I bought turn 6 springs about 20+ years ago as a first suspension upgrade on my '71 240.
I bought them at a long gone parts supplier in upstate NY called Impact Automotive
They were well constructed, had yellow rubbery epoxy coating, and at the time relativly cheap. I remeber that they lowed the car fractionally (about an inch or so), was slightly stiffer than stock. Worked very well as a mild upgrade.
They worked ust fine for what they were at the time. If you're looking for serious upgrades, there's a lot more choice nowadays ... if you're looking for a slight upgrade over stock, they work really well.
Good luck....