Yanmar isnít Briggs.
Besides that if you have the buying power of Deere and want 10,000 widgets the manufacturer will make them custom to your spec.
Another thing is having identical castings with different machining specs is common and has been since the 60ís. A k181 and k241 share bock, head and shroud dimensions, same with som k301, k321 and k341. The power outputs are not the same because almost every single part you donít see is different.