If you can post a link to the site and a brand name for the plane it would help.

A lot will depend on the weight of the plane and the wing loading to determine if the plane is flyable with the 540 motor. As an example, there is an 8' (8 foot) wingspan Telemaster that flies just fine on a 46 - 61 2 stroke motor (actually the 61 is overpowering the plane a bit).