In terms of Mauser model 1898 rifles, there are some differences in the area of the rear receiver bridge, but not major, or they wouldn’t be model 98s. Among K98k rifles, really no variation, as they were a particular sub model of 98s in themselves. ( a fairly small number of receivers were made differently to facilitate their conversion into sniper rifles with scope mounts)
After you make a couple of more posts here, you will have access to the ‘Picture Reference’ section of the forum, and there are photos galore there. Liberty Tree Collectors, a commercial site, has its own (smaller less detailed) reference section that is open to the viewing public.