Sorry, Mike, I have never seen a Harvan. There are a lot of European makers past and present and a lot more importer's trademarks. I think you have good information from Jim K and Johnbt. I would not guess the dollar value. Anybody who says it is worth a lot should have money in hand, otherwise it does not mean a thing.
The gold inlay in the stock is for the owner's initials. Most of the ones I see are blank; I guess people think about resale value rather than personalization.
Markings, from 'Gun Proof in Spain' by Lee Kennett, Gun Digest 1971:
serial # is AB11**. It is only 4 numbers AB is the maker's mark, per that other board. A four digit number following may be the weight of the barrels in grams, not the serial number. Check other locations around the gun for a serial number.
20-70 with a circle around it As I said, 20 ga. 70mm = 2 3/4" chambers.
a knight with a shield with an x in it Inspected and tested at Eibar, Spain.
a shield with a bp and a circle under it inside the shield Proof tested with smokeless powder.
it looks like two brooms making the letter X with a 2 in the middle Proof tested with black powder.
The barrels have the choke as 15.4 and 15.7 with MG over them. Does it SAY "choke" over those numbers? Choke measurements ought to be so marked. If not, those are the bore diameters after the first proof test. Standard bore diameter for 20 ga is 15.6mm. If it says "choke" then you are about Improved Cylinder and Cylinder. My chart does not have "MG" and I do not know what it stands for.
also the markings under the chambers have 850 kgs Test pressure of the smokeless proof test, about 12,000 psi.
mc5 Not in my chart of Spanish proof marks. Maybe a company inspectors' mark.
K1 with a small x over it Ah-HA! That is the date code for 1965. From the Star website, not Kennett.