7x57 would fit the action, sure. I would wait and see how the 8mm shoots, it may well surprise you and there is absolutely nothing wrong with the cartridge.
Lothar Walther used to make a Mauser replacement barrel complete with steps. I don't know if they still do but it would bear checking out if one were hell-bent on re-barreling and retaining the original stock.
I was gifted a Mauser 98 (early war-time BRNO) by the son of the GI who brought it back, who sporterized it some time in the 50's. The bore was (is) as minty as I've ever seen on a military Mauser, and even though I'm not a fan of stepped barrels on nice sporters I elected to leave it alone when I did a makeover on it because it is so righteously accurate. A classic case of "don't shoot the donor" if ever there was one.
As for re-crowning, a crown has to be outrageously screwed up to actually effect accuracy. As long as the bullets leave the muzzle exactly the same each time is all that matters. This has been proven to my satisfaction by men more capable than me.
Last edited by gnoahhh; 07/19/17.
