I have a "Windsor Churchill II" 20 vs 26" made by Zabala that I like as a loaner and a grouse gun. I had a Zabala 12ga so-called "pigeon gun" that was fairly high grade, sold to a chap I used to shoot sporting clays with.
Is that a Zabala Hermanos branded gun or one of the "Matadors" made for Sears. I can see Zabala on the barrels, so I'm guessing former rather than latter?
Zabala, like all of the Eibar makers in the fifties and sixties was less a manufacturer than the financier of a cooperative. They bought in parts from Eibar artisans based on the price point they were aiming for and did final assembly and finish. I am pretty sure Zabala made their own barrels.
So the trick with Spanish guns of that era is to identify the price point being manufactured to. My 12ga was a European market gun and was well finished, well engraved, and had good wood, albeit nothing special. The "Churchill" 20 ga was imported by Kassanar as I recall and was a bit of a scam. Very basic box lock, Anson & Deely set up, with a good set of chopper lump barrels. Moderate engraving in a classic rose and scroll type pattern but with a rather cheesy "coin finish" receiver. Good barrel bluing. good regulation. Double triggers. Choked a tight IC/M. All good to that point. Then, for the "American market", they ruined the gun with a pistol grip and beaver forend. Unbelievable. I don't know what they sold for originally, but I got the Churchill for $325 about 10 years ago. I can't remember what I paid for the 12ga but I sold it for $1800 and will have certainly made some money on it.
If that 10ga is a straight Zabala and not a "Matador" it will likely be a better gun. However, a few things to keep in mind. I can't tell from the photo, but if it's not double triggers, walk away. Spanish guns of that era with single selective triggers are notoriously unreliable and prone to doubling, which will be very unpleasant in a 10 ga. Check the rib. I think I can see silver soldering in the last pic and this is another weakness of mid to low end Spanish guns of that era - poor silver soldering of the ribs. You don't want that rattling loose on your second shot. Pot metal lock work. That 10 ga looks like it may be a better grade, but even my Churchill's internals are a little fishy and in a 10ga, pot metal will not hold up. I really dislike pistol grip and beaver tail forend on a SxS, a real abomination. But in 10ga, I think it's the better set up, adds strength and heft, so that's a plus.
As to value, that's up to you. There's no flourishing market for 10ga SxS, let alone 50 year old Spanish 10ga guns. I wouldn't want one, but if I did, I'd be willing to go $500, providing it's double triggers and the rib soldering is solid.
Hope this helps.