I have mbx pro, which i bought in december.
As far as i know, now MBX pro and lx pro come with the new 26 engine.
They still have same boxes where it says that it comes with the 25, but they put a little sticker on boxes where it states NEW 26 engine.

PS. If I were you, I would not think about selling the engine and getting a new one. There is nothing wrong with the force 26, for me it has been great, not a single problem. Very powerful and runs great.

Sorry about my english, thats my third language.

Have fun, thats a good buggy for the money.