I have an Empire 598, which apart from the arm and electronics, is exactly the same as the 698.
I put a jelco 750 arm on mine, simply dropped it into the hole left by the old one. There is a difference in overhang but it can be solved by moving the cartridge back about 3mm in the headshell, if you can do that depending on the cartridge. I have a boron tipped Denon 103FL mc and it all works wonderfully well.
If you ever need a new belt that is truely the right size have a look at esotericsound.com. They are US based but in my experience their belts are as good as the originals. They also have all kinds of other bits and pieces for empire turntables. A lot of people replace the rubber gromets shown in your last pic, but a word of caution, I tried this and the old ones performed better, so I put them back in. The audiokarma thread has a lot of useful info about maintainance, but if it's working fine less is better, although the occasional cleaning of the spindle with oil similar to 3 in 1 but with a blue label (it's in the thread) is all you need to do, and a minimum amount of oil at that.
Enjoy your turntable, thay are real engineering marvels, cheap as chips but I shudder to think about the cost of something that would be a worthwhile upgrade, relatively speaking.