As you correctly assumed the stamping of the numbers 2 & 4 on the barrel flats designates the choke of each barrel. 2 being the designation for a modified choke and 4 for a full choke.
The short answer is no. I have a Remington Model 1100 Circa ~1963 with a 30" barrel and integral Full choke. This barrel does not accept any additional chokes. You could procure a newer barrel relatively cheaply (roughly $200 new or much less used at a gun show) that will accept screw-in type chokes. Another alternative would be to install an after market screw-in choke system. Not all barrels are candidates, but many are. One such after market installer is "www.choketube.com".
Yes. I have one. Double barrel, hammer gun. Damascus steel barrels. Circa 1895 I think.
Look for similar bikes on Ebay or craigslist, see what they are selling for.
If it is a vintage ring, it may be from the Traub company that made engagements rings circa 1925 and marked their rings with a TT.
The Greek made Dipylon vase is from the Late Geometric Period or circa 800 B.C. This period marked the peak production time of ceramics.
There is no such currency as the 'circa'. 'circa' means 'approximately'.
Value is too difficult to be accurate without seeing the gun. Condition which includes the amount of original finish and original configuration will determine value. Auto 5's with recoil pads (other than Mag 12's) poly-chokes and compensators will reduce value. Expect $250-$800 range for this gun. Recommend taking it to a gun shop for appraisal.
A c means circa or around, so when an event is shown as c150 BC, it means it happened around 150 years Before Christ.
What condition is the pistol in? Also is it still working? These two factors determine the value.
'circa' may not be a currency at all; if your referent says 'circa', it may mean 'about'
No, circa does not need to be capitalized.
"Circa" means 'around.'