Contact Ruger customer service through the Ruger website. Soem parts will require the rifle be returned to the factory for fitting.
100-1000 depending on specifics
You will have to define what you mean by "best". Is your primary objective recoil reduction, blast reduction, or a combination?
Manufactured in 1987. For specific month, you would need to contact Ruger. For another question about it to be answered, you would need to give a specific question.
We can't tell without the serial number- but if you go to the Ruger website, under Customer Service, you can see the year of manufacture for serial numbers. You will need the spefic model of your rifle.
Ruger's website has extensive sn data.
100-500
Depending on condition, and WHICH version of the M77, between $250 and $500.
Unknown caliber. Contact Ruger
If the Ruger website is up, it has sn data.
The Ruger website, under customer service, historical data, rifle, M77, will have the serial number ranges for each year of production.
100-400
Remington 700 308?