I received an amazingly fast response from Vector Flight's customer service. Here is their response:

"Thank you for your message. About a year ago when we first introduced the Edge 540 66, we recommended a 90 4 stroke as the max.engine size. Inevitably, many customers started installing larger engines, including 100, YS 110, and even 1.20 4 strokes in this airplane, with great results. In response to this trend, we added several reinforcing structural members in the design to make the airframe adequate for the larger engines. Now we believe a 100 or 110 4 stroke is optimal, therefore if you do have a choice, we would recommend using a Saito 100 instead of the 90!"