The Horizon is a great table - one of the best at its price point. But, it is of a different design than the Interspace, Spacedeck, and Hyperspace. I've never heard an RS arm on an Interspace but I do know that Nottingham will build for you the appropriate arm pod for nearly any arm. Since these tables will accommodate two arms, there may be three ways to go. One, you can buy a whole new arm pod and mount your existing pod on one side and the new pod on the other. That route, a new pod, will cost in the neighborhood of $350. Or, if you want to use just the one arm, you might be able to get by with buying just the small arm pillar and mounting ring and then affix it to your existing pod (depending upon arm geometry). That will coast about $150. Finally, if the arm has geometrics similar to a 'Not or Rega, you might be able to get by with just a different split-ring collet to use in your existing arm pillar - about $35.
These are options to look into. In nay case, the Interspace is a solid choice and can be had a good prices on the used market, especially.