Please don’t take personal offense, but I’m going to criticize your rifle a bit. (& maybe burst your bubble)
All rifles “processed” by Mitchell’s Mausers are refinished rifles made from non matching parts & renumbered to “match” but they are like a repainted & restored ‘57 Chevy Bel Air coupe, look cool, are ‘real’ firearms but NOT a real German WW2 K98k rifle, and their value is comparatively low, because of what Mitchell does.
1st off, its a post war Yugoslav made rifle (Zastava Arms) made in a length never used by any German soldier EVER. There’s ‘no such thing’ as a ‘tanker rifle’ in terms of German K98k rifles & German tank crews. Machine pistols, yes, carbines shorter than a K98k, no. that’s pure sales & marketing fantasy. Yugoslav tank crews might have used them in the 1950s-60s, but not German panzer crews in WW2.
The history is that Don Mitchell made a business & brand out of buying surplus rifles & refinishing them, & in the case of K98k rifles, issuing a made-up “certificate of authenticity” that is meaningless. When they ran out of genuine russian capture K98ks they went to more available similar rifles like the M48 & M48a models. I hadn’t seen a Mitchell’s M63 before, decent pix for your 1st post here.
“Never fired” is a marketing idea, all firearms are test fired before proof marking & offering for sale. All countries around the world, no exceptions. Not fired since refinishing, & so ‘unmarked’ definitely.
So value? I’m sorry, but likely less than you paid unless it was cheap. Resale? If say someone wanted it for their office wall, perhaps the best opportunity, or as an 8mm shooter? Perfect for burning off some 8mm ammo, but little or no collecting value.
I sincerely hope that you stick around, there are good collectible rifles for sale here regularly, at entry & higher levels. Look thru the Photo Reference section of the forum to see what collectible rifles look like, & ask questions before you buy the next one.