First, I have a Redfield model 70 all steel receiver sight for a Marlin 39a (as indicated by the 0 on the back of the arm). These are built like tanks and are relatively hard to find. The sight is in great condition and would be a perfect compliment to your vintage 39a. $80 shipped. SOLD PENDING FUNDS
Next, I have a Lyman 56 LA receiver sight for a Marlin 1895, 1894, 36, or 336. This sight is all steel, unlike the newer model 66 LA which has an anodized aluminum body. The LA series is designed for Marlin 36, 336, 1894, and 1895 rifles. This sight quite possibly would work on other flat sided receivers, such as the Winchester 1892, 1894, 65, 55, 64, or 71. The mounting screw hole spacing between the holes from center to center is 14/32nds or .4375". These sights are hard to find and are relatively collectible. The sight is in great condition. $125 shipped.
I accept cashiers checks, money orders, and paypal (add $4 to help cover fees). I'd also consider full or partial trades for a Leupold
6x fixed power scope. Please post an I'll take it here. I also have the sight listed in one other forum so I'll use time stamps to determine priority. PM me with trade considerations.