That completely depends on the stock/chassis the action is in. This is an AICS pattern magazine so your stock/chassis would need to accept AICS pattern magazines.
A mini action [ what you have] is smaller. There's long , short, and mini sized actions,
No. These are for short action calibers (.308 win, .260 rem, 6.5 creed, etc.) you’ll need one for 7.62x39 / 6.5 grendel unless you have a custom chassis, in which case only you would know.