Many of these older pattern planes weighed 9+ lbs. due to heavy glass and paint finishes as well as electric retract systems like the Kraft units. I see no reason why they would not be able to handle a light 4-stroke like the Saito 1.00. Also keep in mind that the Saito, while a powerful engine, will not fly the model at the speed any of the Rossi or OS VF engines did so the stresses upon the airframe will actually be lower with the Saito.

John