Well, there is always the brute force way of figuring out what size it is, but I can tell you it is NOT a 25. I have owned every model. Forget the numbers.

Why not bench run it. If it won't turn an 18 X 10 worth a hoot, which is recommended for a 41, then it must not be a 41.

If it purrs with a 16 X 8, it is a 25. (but I say again. it is not a 25!)

Bench run it!

Also, the 25 has a completely square head, looking at all the cooling fins from the side. The 35 and 41 are not square, looking from the side. See the picture I posted earlier.

Bill