My GM column has splined out put and my MII rack has splined input, but not the same diameters. I will likely convert over to a double D sectional one day but no plans at this time. Cost is usually no different between splined shafts or double D's. Stainless is a lot more expensive than steel for everything, shaft, u joints, supports, vibration dampers etc.

As volksrod said the advantage of the double d is being able to cut to size. With the splined units it's like carpentry...... measure many times, cut once.

I have seen vibration dampers in use, but I don't have one on my car and don't think I have a real need for one either. I know Borgeson has everything in steel or stainless, but I thought Flaming River did as well, but I see that they now only offer stainless and aluminum.

Mine had Mil-Spec universals for years and never had any problems even though they are not street intended. Good enough for airplanes and drag cars, but not for street rods.