The "C" serial number prefix will probably put it somewhere in the mid to late 1970's. I'm guessing they skipped the "D" prefix as it could to easily be confused for a zero (0), and the "E" prefix guns ran through most of the early and mid 1980's until Savage filed for bankruptcy and Ron Coburn came in and took things over.

When the Gun Control Act of 1968 was passed and required all guns to be serial numbered is when Savage adopted the letter prefix for their serial numbers and they went in order...A, B, C, and so on. Savage just started using the "H" prefix in January of 2010, and the "F" prefix ran from 1989 through the end of 2002, so the number of years a particular letter is used isn't consistent.

Jeff's correct on the barrel not being easily changeable as they are threaded and shouldered barrels and each would have to be indexed to the receiver for proper rib and magazine ring alignment. You can get a new replacement barrel from Numrick's, but it would have to be custom fitted to your receiver by your gunsmith and you'd likely have more in the new barrel than the gun is worth when all was said and done.

If you can live without the vent rib there's a chance you could have the factory barrel machined to accept choke tubes. I know there's a guy up in New England that does it and is highly recommended by the folks over on the Shotgun World forum, so you might want to ask around there.