I've had a Peterson Shape 69 on my wish list for a while and recently scored two pipes. One is a 1974 hallmarked "Sterling" and the other a pre-Repulic "Deluxe" with the X69 designation.
Mark Irwin tells me that he believes the X stamp was given to pipes with the same size bowl dimensions, but larger outer dimensions. The Deluxe is indeed significantly larger at 61 grams, versus 43 for the Sterling.
The Deluxe is too large for me and was sold.
More details and pictures of each pipe are in this Reborn Pipes blog entry.