This is my best guess,1st these cars aren't coded for 383's on the vin tag,only on the data plate and then only in the engine option box.The reason for the "M" designation on the vin is that the Dart line was never available with a 440 as a standard option,so I'm assuming that MoPar instead of using the regular B-body vin code for 440 they just decided to use the "M" code to designate these cars as special order/special build.The reason for the 383 coding is the rest of these cars are identical to a regular build 383 car,w/o the availability of a few regular 383 options. 2nd,the clamp on the steering box,I really can't answer this one,but all I can say is that there is a part# for it in the 69 parts book for usage on all car lines and models,and I have personally seen these before on some pick-ups. Anyone else with a theory.Here's a pic of my M-code GTS. John.