The plans for the Akromaster shows an unmuffled Fox .15X (slant plug). The plane's size was designed for that type engine. Modern (or even old) engines using a muffler moves the balance point forward. To compensate you add tail weight. All of this adds up to a higher wing loading. The larger wing provides a lower wing loading.
The lower plane in my pic has a Fox .15X with muffler. The upper plane has a TT .10 with muffler...probably about the same weight and power output.

George