Tower knows what they are talking about. They are a branch of the importer of both OS and GMS. The GMS 76 is 19.4 ounces without the muffler. A 60-76 size muffler will weigh 4 to 6 ounces. That puts it right in the ballpark, most 61 and 75/76 2-strokes with muffler, weigh right at 24 ounces.

No, I wouldn't add that much weight to a 40 size airplane. It would make it really twitchy. I'd use an OS 55 or a Saito 82. Either one of those will give it better overall performance than the 76.

Jim