Ah, that may well be the case. The auction I remembered was for a 59/66A1, and you could just make out the difference in the color of the steel. I thought this modification could be corrosion-related since I've got a hard-used M59 with advanced pitting in the area of the "extension" from poor maintenance. I was never able to get clearer images from the seller, but I'm guessing this may be what was on the rifle.