D5's are stamped either with the D5 or just the 5. The 6 is usually stamped upside down and they are normally 1639 stall converters. Can be made to stall similar to a D5 with the proper stator and someone who can rework the fins. Better off getting the right converter first. I used to have stacks of "6" converters that I had converted to D5 specs and they never worked like a real D5 did. Just slightly off so I quit having them done.