The differences between FN-Browning CCS25 and CCS525 having been discussed in details before, I think it it best to reproduce my (lengthy) earlier post :

Browning O/U CCS 25 double rifle

Presently, Browning is marketing 2 kinds of O/U rifles :

1. the real McCoy, called the CCS 25 and based on a specially machined 20 ga action forging. The bottom of the action is not hollowed out and the side walls are much thicker than on a shotgun. To illustrate my point, here's a pic of a B25 12 ga receiver (L) compared to a 20 ga sized rifle receiver (R) :

The double rifle also on its right side is fitted with 2 hollow gas screws to divert gases from the shooter's face in case of a primer/case rupture (see pic, the arrows point to the gas screws masked by the engraving) :

Barrel regulating is the classic (and expensive) wedge moving/soldering + test shooting (see pic) :

Standard calibers are : 30R Blaser, 8x57 JRS, 9,3x74R. When properly done, the rifle is extremely accurate. Here's how my 9,3x74R groups both barrels at 50 m (scoped & elbow rest) :

Being >90% handmade, the CCS 25 is expensive. 2009 retail prices go from 9.600 € (12.000 USD) to 15.750 € (19.688 USD), according to grade. My rifle, a B 5 "middle of the road" sells for 13.500 € (16.875 USD). It is possible to have a 100% custom rifle built to one's fantasy (cost ?!?).

2. the "look alike" CCS 525, built on a 20 ga B 525 shotgun action. Fully mechanized production, it's a nice, well made rifle. Bbl. regulation is easily (self-)achieved via a sliding ring between muzzles. Economically priced at 3.399 € (4.249 USD) - 3.659 € (4.574 USD),it's a working rifle which competes with the Beretta, Chapuis, etc. line but can't pretend to play in the same ligue as the FN CCS 25, Ferlach or best quality English rifles, but then it costs 1/3 of the latter's price...

For more info, have a look at :
http://www.browning-int.com/intro.html
*Browning - double rifles - CCS 525
*Custom shop- double rifles - CCS 25.

Now regarding the .270 rifle you're contemplating, you'll be able to confirm its origin using the above indications. However and basing myself on caliber and period, my 1st guess would be that it is indeed a genuine CCS25, part of a special USA destined shipment. These rifles were known as the "Continental" model and were chambered in .270 Win and .30-06.