I have a feeling that the cheif limit of axle travel on an 88" series rig has more to do with the tyres hitting the wheel boxes, than the capability of series springs to allow articulation...
This is a std 109" with Station wagons springs, slightly rusty... it would almost certainly do better with a bit of grease on the springs, and probably swaping to standard springs would also get a bit more...
I don't see that you could do much better than the rear with coils, as the wheels would be hitting inside the arches...
