That Savage base used Leupold Standard rings. https://www.opticsplanet.com/leupold-std-rings.html
The Leupold Quick Release Rifle Scope Rings will work if you have a corresponding Leupold STD Base that fits that muzzleloader.
These Leupold Quick Release Rifle Scope Rings mount to the Leupold Quick Release mounts and will not work with a Ruger American Ranch. The Ruger American Ranch in 350 Legend comes with a picatinny scope base installed, so you will need rings that are compatible with that rail. I recommend using the 1 inch diameter medium rings located at the link below for that scope and rifle.
https://www.opticsplanet.com/leupold-backcountry-cross-slot-30mm-rings-med-matte.html?_iv_tube-diameter=1-in&_iv_ring-height=medium
Yes, as long as you have the matching Leupold QR bases.
Extended rings allow you to move the ring either forward or backward of the normal mounting point to accommodate longer or shorter mounting areas on scopes. They are typically used for long action or magnum action rifles.
Per Leupold, yes it will.
Item 49973 are the standard rings, while item 49983 are the extension rings.