the mast jacket is the cover piece of the steering column ["steering mast"] - the 67-72 switched to a whole new shifter setup from all the previous series trucks, integral with the mast jacket instead of being mounted external to it ... it should be pretty easy to determine if anything is actually worn to the point of needing replacement, like maybe some metal grommet-like critters that are worn out [including at the trans arm/rod connection], otherwise if you have someone hold in the clutch and move the shifter thru the gears as you watch under the hood, it should all be pretty clear
Bill
