I would need to know the serial# and two letter date code stamped on the barrel to be exact, but these have been imported since 1979 under several store brands as well as the investarms name and are still sold today by Lyman and Cabela's.
You will need a professional appraisal
Yes
Unknown.
Stevens.
Remington
Take the rifle to a gun shop so they can figure out what make, model and caliber rifle you have. There is no 84 caliber long rifle.
Springfield Armory
H&a
They were made in several calibers- will be marked on the barrel.
WHICH rifle? There is more than one type made in this caliber.
The .950 JD Jones is the largest sporting rifle caliber made.
The REAL ptrs41 was a gas operated semi auto antitank rifle first made in 1938, and was approximately .55 caliber.