You may have to redrill. It is no big problem. Take the old one out, and find one that's close at the local hobby shop.. Or, you can get one of the Universal type that mount the engine in a strap. Not the best way, but I have 2 like that, and they have been more than adequate.
You have a great trainer, and now a great engine to go along with it. I just wore out my last evo 45 trainer engine, and used a Magnum 52 four stroke to replace it. It's not as fast, but I like the 4 stroke sound, and it really is enough to train with. As long as you mount it even close, it will work. Of course, the closer you keep it to center, the better. The 1 or 2 degrees of offset thrust is already in the firewall, you shouldn't have to worry about that.