My 69 Z28 muffler has only a "W" on it with no other letters or numbers. The V notches are exactly the same, they were not cut. The GM Box was very badly deteriated when I got it late 90,s, so I dont have a part number, but it was identical in size/shape to the walker aftermarket muffler the car had on it since about 84?
1 of the other NOS mufflers also has the "W" with no other letters or numbers at all, it is in a GM box with part number # 3981951 on the box as well as the box is dated 9-22-70. It has the small slits in the inlet tubes as previously posted . GM parts book says this is a 67/68 muffler, my book shows 69 as #3961396 which supercedes to #3981951. The other NOS muffler is buried in a shelf of parts, cant get at it rite now. The posted pictures are of the muffler on my car.
Hope this Helps.