Your Mossberg was made from 1960-1971. Serial numbers came into being for those rifles in 1968 (earlier, not required). Takedown is almost instinctive, but can dig you out some instructions if you need them. Based on the earlier Mossberg 152K design.
Your Savage/Springfield/Stevens was about 1965-1981. Here is a schematic- http://www.gunpartscorp.com/Manufacturers/SavageStevensSpringfieldFox-33479/Shotguns-40503/18C-41274.htm?results=All
Extractor is the little sheet metal bit at the front of the bolt (part 10) ejector is the little wire looking doodad- part 12.
Reference shorter shells- with the exception of a few autoloaders (Remington 1100 comes to mind) can shoot shorter shells than marked with no issues. HOWEVER, while a longer-than-marked shell may fit, THOSE can be very dangerous to fire. With a shotshell, on firing, front of the shell OPENS. There is a space designed for it to open into. Too long a shell, it opens inside the forcing cone- no room for it, spikes pressures.
Be sure to clean well under the extractor. They are sheet steel and DO wear, but crud is the #1 problem.