The easy way...
Woad-Yurt--Too late to return the rifle to Mitchell's Mausers and get yr $$$ back? If so, then you're stuck with a rifle without very much collector value.
You said it shoots well--there are replacement rear sights that don't require any modification, and are far better than the original for accuracy. Have you considered going that route?
Anyhow, the way to get a 'scope on a K98k Mauser, WITHOUT affecting its future collectibility (hey, some day there won't be any more of these, Mitchell's or not, and at that time the price of all of 'em will go nowhere but up. Even Mitchells.) is to mount a so-called "scout 'scope".
You buy a special mount that replaces the rear sight with no gunsmithing--B-Square sells one; there are others--and also buy a "scout 'scope" which has the necessary 10" or so long eye relief, mount 'scope on the mount, boresight, sight it in, and there you are. An added benefit is that you don't have to modify the bolt handle nor the safety.
Voila! A 'scoped K98k, which can be returned to its original condition, whenever wanted, in about 20 minutes. Be SURE to save all the little pieces of the original rear sight.
I did this to a M-48 Mauser that I put in a sporter stock and added a Timney trigger. All reversible actions, although the M-48 will never be as collectible as the K98k. I'm not looking to sell it, ever, but you never know. It puts 200 grain Accubonds into < 1.5" at 100 yd, and < 3" at 200 yd. No target rifle, but it'll do just fine for feral hogs.
If you really want to 'scope a K98k, with drilling and tapping and a "regular 'scope mount", plus safety and bolt handle modification, there are lots of 'em to which that has been done since GI's first began bringing them back in 1918. Lots more bring-backs in 1945. Almost any gun show will have such available. I'd look at trading my Mitchell for one of those were I you--for 2 reasons: (a) the Mitchell, unmodified, will go up in value to an extent--some day. Once drilled, you've lost that option. (b) why re-invent the wheel?
Keeping firearms that "might some day go up in value" strikes me as a very risky investment. You would do far better with the same money in the stock market, or even in a CD. Unless we're talking firearms that cost a couple of thou in the first place--those beauties might be a good investment, but your Mitchell, and all of my firearms for that matter, are decidedly not in that class. That said, I still would not modify an unmodified K98k, even a Mitchell. But that's MY opinion, and we're discussing YOUR rifle.
Do what feels "right" to you. I for one won't criticize your choice.