has anyone thought about adapting the 18 wheeler type air ride cab mounts to an AD Chevy truck?
Yes, and I decided it is not worth the effort. Here are two ideas and considerations.
1. The connection between the fenders and the cab, and also the hood to cab needs to be very flexible to allow the cab to move. I could not think of a good, reliable, and simple way to do this, and still have the truck look good.
2. All the sheet metal, cab, hood, radiator support, and cab could be made on an air ride. There would be one hinge under the radiator support, then a sub frame from there back to the cab mounts (three in your case). You would need some room between the fan and the radiator, but that's probably not a big problem. The bigger problem is getting the sub frame to fit just above the frame and under the cab and all the sheet metal, and clear the steering box too.
I have a 3" body lift on my truck to help fit my transmission and engine, which would make about enough room to have a sub frame for the sheet metal. In the end I decided it was still a lot of work for not much improvement in ride, and you gain a number of small complications. Another way for a smooth ride is in the regular suspension, and I have springs rated for about a 1 ton, or just a little stronger, those combined with adjustable air "helper" springs should allow me a reasonably soft ride when empty, and the capacity I need when loaded.
Eventually I would like to have a full air ride rear suspension, probably a Hendrickson HAS-120
http://www.hendrickson-intl.com/products/product_detail/has_single.asp. Or perhaps this one from Kelderman http://www.keldermanairride.com/productdetails.php?id=450%2F550FRD4LNK But I'll give th truck a try for a few years with the current suspension before I tackle that swap.
Grigg