It does seem to be an oddball size - I'm not aware of any lifts with plates that size. But, since you have a router, you can fix it by enlarging the opening. Beats the alternative of throwing it away. Basically you are going to route a slightly larger rabbet around the edge of the opening. The good news is it's fairly easy to do.
First thing to do is to decide which plate size you want to use - 8 1/4 x 11 3/4 or 9 1/4 x 11 3/4. I'm guessing you will want to go with the rockler (8 1/4) opening. Rockler has the incra/jessem Mast-R-Lift II on sale right now though you can get by with a lesser lift.
There are several ways to go about enlarging the opening. The two I can think of use a template. One uses a pattern bit (straight bit with a bearing on the top - closest to the router), the other uses a bushing and a straight bit. The pattern bit approach is easier to explain.
First you need to have the lift in hand. Lay the router lift upside down on the table exactly where you want it to be - I'd suggest centered over the existing opening. Then place 1/2" thick MDF strips against all 4 sides of the base so there are minimal gaps at the corners. I'd make the strips at least 4 inches wide, maybe even more. Use double sided tape to hold the strips in place. Now, you need to have a pattern bit that has the same radius as the corner of the lift plate. You chuck the bit in your router and lower the bit so that the bearing sticks down so at least 1/4" rides on the template. You will need to get a pattern bit that will allow you to make the right depth of rabbet. That depth depends on the lift you get. It's cutting length will need to be a bit less than 1/2" (for the template) + the plate thickness. For the MRL-II I think it's 1/2+3/8 so a 3/4" cutting length. Then you just route away the excess material taking small cuts - say 1/8" - per pass.
When you get your lift, you'll get lots of help here. I'd practice on a different piece of wood until you get confident.
edit: You did ask about lifts but just to muddy the waters, another approach would be to get a plunge router that supports "above table adjustment". No lift needed. Might be a cheaper approach if you don't already have a router and you could probably use the plates that came with the table.
Last edited by PhilBa; 07-12-2015 at 11:48 PM.