I have a Sarasqueta in the same caliber too. As you can imagine, they are not unusual in Spain. If you drop some photos of the marks under the barrels, it should be easy to tell you when it was made.
Sarasqueta was probably the better known of the spanish gunmakers producing double rifles in a great number of chamberings, un to 577NE. The firm had a long and complicated history, and produced very good and not so good rifles. I think a good number of double rifles arrived to the USA at the beginning of the 70s, maybe yours is one of them.
I think you should fire it and see how it was regulated. And try more than one weight of bullets. Sometimes it were regulated with relatively light bullets, and used in our driven hunts. We did not really need shooting 300 grains bullets for a spanish boar!
Mine is number 97745 and was made at the beginning of the ´70s, has chopper-lump barrrels and weights 8,75 pounds. It has relatively thick barrels and initially shot very small groups with each barrel, but 4-6" apart at 50 yards, so I had it re-regulated with Norma Oryx of 300 grains. I also re-stocked it with Spanish walnut (what else...?)
Here you have some photos.