[JT-AR-MG42]

To remove it, use a non marring punch ( or the tip of a cartridge, it was designed for one ) and push in against the spring pressure on the 'hole' at the rear of the floorplate. At the same time, pull the punch toward the triggerguard - to the rear - and floorplate with the spring and follower should be free.
To re-assemble, center the floorplate up, push down on the whole of it and push forward. You'll hear it click into place.
It will be much easier the second time after you have all the grease out of it.
As to shooting it, remember that almost ALL imported 8mm has a corrosive primer. No problem, just remember to use several patches and brush strokes of HOT, soapy water after regular cleaning and before oiling. Bore and bolt face.
As to value, RC's are becoming more collectible, especially the more rare production codes. It is interesting how much AC's ( American captures ) have risen when one considers that roughly seven in ten of the so-called bringbacks are actually pre-68 imports.
Oh well, who can predict market trends. Certainly not my mutual fund manager!
Good luck with it, and enjoy your freedom to own it! JT