In regards to the bayonets, just about anything of the period might have been issued to the soldier the rifle was issued to, during it's service life. On the G98m, you said it was not a post-WW1 reissue, so more than likely a S98na would be appropriate. For the Kar98a dated 1915, a S98/05aa would be nice, but these can be a bit difficult to find now, so a S98/05na would work as well. I omitted mentioning the sawback patterns of both bayonet types as these, too, have gotten quite pricey.