yep ... choate
Pistol
No, the Remington Model 1100 stock has a hole (recepticle) through the inside of the stock in the pistol grip area to accept the action spring tube. The Remington Model 870 stock has no need for this hole so the 870 stock will not fit on the Model 1100 action.
Available from the Remington Custom shop- Model 7.
Remington's website has what you are looking for.
There is no Remington Model 6 pistol, there has been however cases however of Remington Model 6 rifles converted to pistols by gun or "home" smiths. NOT Remington. As such the value is whatever someone will pay, but generally not much.
What Model 51 pistol or a rifle and what model?
Action size.
Yes, The receiver pins are the same as the Remington 870, so any stock that will fit the 870 will fit the 7400
Action size.
A Remington Model 700 chambered for the 7mm 08 cartridge would be a short action as the cartridge is based on the .308 Win.
Remington Model 12 barrels are threaded to the action. Barrels can be replaced with the proper equipment.
Click on the link below for photo Model 51