There's no reason that it shouldn't still be dependable after 40 years if it has been stored properly and cleaned after usage. Problems with rust can develope if any firearm is stored in an enclosed gun case that does not let moisture evaporate away from metal surfaces where rust can develope. A light coating of oil on the metal surface will go a long way to protect the bluing.
Remington discontinued the Model 760 rifle at the end of 1982 and introduced the Model 7600, Model 76 (cheaper version) in 1983. Yes, it is still being made.
The Remington Model 742 was made from 1960 until 1980, and it was replaced by the Model 7400 in 1981.
The Model 1100 has been made since 1963 and is still in Remington's catalog.
Yes
They still make a synthetic stock for a model 700
They made them in four calibers. 25 Remington, 30 Remington, 32 Remington & 35 Remington. The 25 & 32 are obsolete, the 30 was still available in the 80's & the 35 is still available at your larger sporting goods stores. There are dozens of custom reloaders that will still supply ammo for any of these calibers.
Production of the Remington Model 552 A, Speedmaster began in 1957 and was still being produced in 2006 as the 552 BDL Deluxe Fieldmaster NRA Edition.
That's still available from Remington, you probably have to register on line and request an obsolete manual. http://www.remington.com/library/downloads/owners_manuals.asp
Had me for a minute the model 6 is an old rolling block the model "Six" is a modern variation of the 7600 and no they stopped making it in 1987.
No 35 Remington fired only 35 rem. The 35 Remington is a good cartridge, it's a little more difficult to find but it is still being made.
They are all still made in Illion, New York, I believe.
All nickels are still worth 5 Cents