CG is not the determination of what engine can be used. You can always add weight or better yet shift weight. You can put a v8 in the nose and with enough weight in the tail make the cg right. As you can imagine, the needed weight to offset a v8 will make the plane too heavy to take off. The consideration then is wing loading. Wing loading is the total flying weight of the plane divided by the square foot area of the wing. As wing loading goes up the plane's stall speed goes up and its ability to "float" decreases.

The Tango has a published weight of 5.5 to 6 pounds. It also has a published 747 square inch of wing. Using the lower end of the weight this makes the wing loading about 17 oz per square foot. A good target weight per square foot for a sport plane is 20 oz per square foot. If the plane comes in as published it has a nice wing loading.

I would think that this size wing could support the above engine weights. What would help is if someone could give the weight of his plane without the engine. We then can add in the weight of the desired engine and do the math and see what the wing loading would be. A simple rule of thumb is 1 pound of plane for 100 square inches of wing, so you can see that the tango can support more weight and stay under 20oz per square foot.