I have one in a 74 C20. I haven't put many miles on it yet as I just changed out the rearend to better suit the diesel. They are noisier than the 6bt, shaky as wrenchbender mentioned, and pretty poky in stock form (mine is the 105 hp version). They have mucho potential as Tango said. I hope to get high 20s fuel mileage on mine.
