Beware of scammers.

How did you get Jan 1970? If the date code is BX it is January 1973 or 2003, if it is XN it is December 1966 or 1993. To my eye that receiver is much older than that barrel. With no prefix to the serial number, it is pre-1968.

The 16-gauge barrels I know have a very distinct taper for about 3/8 ...

Looks like a late Model 31 TC with the alloy trigger group, a non-original recoil pad, that has been buffed and reblued and got some after-market engraving on the receiver.

P.S. You have posted this in the "Remington Handguns" section.

With the Damascus barrel your gun is a No. 3. From the 1898 Remington Arms Co. catalog --

You are correct. A 16-gauge receiver put in work during November 1940.

Scanning Guns International today I spotted a vent rib The Sportsman Skeet Gun, serial number 784888, with an LUU barrel date stamp.

https://www.gunsinternational.com/guns- ... =103051758

That is a new highest 12-gauge serial number for me. LUU is February 1949.

The new guns the Model 11-48 and Sportsman-48 didn't actually appear until the 1949 Remington Arms Co., Inc. catalog.

Serial number 225546 would be a Model 1889 from 1902 according to the serial number chronology the late Charles Semmer constructed from surviving shipping records, for his seminal book Remington Double Shotguns . No production records have been found. From a 1901 Remington Arms Co. catalog --

1901 ...

If it has the two hex-screws at the bottom of the breech face it has the upgrade.

Old Researcher has been chewing on this a bit. We know from the old "between the Wars" factory ledger that Model 10 production had reached serial number 172939 on September 30, 1919, with the first entry in the ledger. The Remington Repeating Shotgun first appears in the 1908-09 Remington Arms Co ...

The R prefix to the serial number began in 1990 and ran for about five years.

The stock with the swivels smacks of a Winchester Model 70.

Looks like a Model 12C "Target" Grade to me. From the 1915-16 Remington Arms - Union Metallic Cartridge Co. catalog --

A righteous Model 32 TC would be marked as such on the bottom of the frame --
The barrels on the gun could be a set added at a later time?!?

The Model 32-TC "Target" Grade was by definition a ventilated rib barrel gun. The options of 28-, 30- or 32-inch barrels. From the March 1, 1934, Remington catalog --

The Model 31 receiver with serial number 8565 was put in work during the last week of February 1932. I would suggest that the Model 31-T was a carryover from the Model 10-T "Target" Grade --

Model 10T Target Grade, Remington Arms Co., Inc. 1920-21 catalog.jpeg

and the Model 29-T "Target" Grade ...