Geoff some of those old tables were meant to fit a specific router, especially some old Sears tables. I don't know if that one was. Most newer tables go with a removable plate but that doesn't appear to have one so to mount a router of your choice to it you'll need to dill holes to match the pattern on your router. Most of us do that by taking the thin black plastic base off the router and use it for a template to mark the pattern.
A lot of us use the Grizzly plate because it's cheap ($13 when I bought mine). They don't come drilled for any router so you have to. Insert plates all come with one or more snap in rings to limit how much much space is left open around the bit. The smallest of the rings is usually sized so that it will accept guide bushings for doing pattern routing. We normally use those and bushings or centering tools or cones to center the router in the hole before we drill the plate. Unless you have one of those reducing rings that is sized for using template guides for your table then it's not an issue. You'll just need to get it as close to center as possible.
A large percentage of the members on this forum built their own tables. We have a long running thread showing some of them and it might be helpful to you to see what others have done. You can see it here: https://www.routerforums.com/table-mounted-routing/17212-wanted-pictures-your-router-table.html
A lot of us use the Grizzly plate because it's cheap ($13 when I bought mine). They don't come drilled for any router so you have to. Insert plates all come with one or more snap in rings to limit how much much space is left open around the bit. The smallest of the rings is usually sized so that it will accept guide bushings for doing pattern routing. We normally use those and bushings or centering tools or cones to center the router in the hole before we drill the plate. Unless you have one of those reducing rings that is sized for using template guides for your table then it's not an issue. You'll just need to get it as close to center as possible.
A large percentage of the members on this forum built their own tables. We have a long running thread showing some of them and it might be helpful to you to see what others have done. You can see it here: https://www.routerforums.com/table-mounted-routing/17212-wanted-pictures-your-router-table.html