The stamping on the front is a bit uneven but that is not unusual with Selmer stamping. The neck has no pulldown but the left side, in the area below the pip, is not smooth and shows signs of dents being taken out. Fit and played with several Selmers. Certainly offered something strong and interesting. The neck measures at 24.5 mm on my calipers.
You may get a slightly different reading and it may need modest sizing up or down for a perfect fit. The item "Vintage Selmer Mark VI Alto Sax Neck-Gold Plated" is in sale since Tuesday, July 21, 2020. This item is in the category "Musical Instruments & Gear\Wind & Woodwind\Band & Orchestral\Saxophones".
The seller is "jwsaxophone" and is located in Quincy, Massachusetts. This item can be shipped worldwide.