And forget about the 458. Watch the cartridge length if you don't want to modify the bottom metal.
The loaded length of the .458 is .09" longer than the 8mm Mauser. Mag length is usually NOT a problem.
I have an Argentine 1909 converted to .458. It's fine.
somewhere back in the 80s the market value of sporterized (to any degree) milsurps began falling and today its way low, often much lower than the cost of having the work done decades ago. today's buyers want either completely military issue condition, or they want a commercial sporter most often in stainless and synthetic.
IF you're looking to turn it into cash, I think you'd be lucky to get $500 and might not find any takers for over $300 these days. Only those of us who can appreciate the work and the thoughts and craftsmanship that went into sporterizing, to different levels might be interested.
You've got a Yugo Mauser 98, (not the Yugo M48 which is a mauser but the action is slightly shorter than the model 98) in decent shape, but not GI issue and there just isn't any serious market interest for those. And, today, the cost of having a competent gunsmith significantly improve it will buy you a commercial sporter, maybe even a couple of them.
You could get it drilled and tapped and a scope safety installed for a (mostly) reasonable price, but the extra work needed to turn it into a magnum caliber would be much more, and more than the rifle will bring if you sold it.
Its not a bad rifle, its just not what most people want these days.