The GEW 88 is an oldie, figure 1890-1920 and they made a lot of them, in a lot of varieties. Lowest pressure guns of stuff chambered in 8X57 and bores varied in diameter. No reason you can't shoot it though, slug the bore to check diameter and keep the loadings on the low side.
Look for an S marking on top of the receiver. That means it was converted to use the .323 spitzer round. I have one and I try to stick with Romanian surplus since it's a little milder than Turk or Yugo. Doe yours have the barrel shroud?
No, but it bears a great deal of responsibility for the Mauser as we know it. After losing the 1888 competition to the G88 Reich's Commission rifle, Mauser was said to have been so furious that he set out to design the perfect rifle with a ruthless vengeance. Having achieved significant accomplishment in such a frame of mind, the legend sounds perfectly plausible to me.