One of the best cartridge matches for the 698 is the Empire 4000 DI, DII, or DIII cartridges. Many 698's came equipped with the 4000 DII when sold new. The only difference between the three versions is the compliance of the cantilever suspension, the DI being lowest compliance, the DIII being the highest compliance, and the DII in between. All three have the same lightweight cantilever and a very high quality Shibata-like diamond profile (called the "3 Dimensional" stylus by Empire).
NOS examples come up for sale from time to time in the $200 - $300 range. Try posting a "wanted" ad here on Agon.
All three versions will work great with your 698, but the DII and DIII are preferred. Just make sure that the stylus is a genuine OEM Empire 4000D stylus, having the correct housing color and Empire markings for that version. All non-OEM and aftermarket styli are grossly inferior in sound quality compared to the genuine OEM styli. However, aftermarket replacement stylus providers like Astatic and Transcriber often packaged genuine OEM Empire styli in their own packaging, so don't shy away from those, given that the housing has the correct Empire color and markings (EMPIRE embossed and painted gold on the stylus guard) and the packaging says something like "A Genuine Empire Scientific product" or similar.
Good luck.
Dave