A O.S 46 AX weighs 17.2 oz with muffler , a Saito .72 weighs 16.6 and the Saito .82 weighs 17.6 both with mufflers. I have all three engines. Have had both the O.S .46 and the Saito .72 in a the same plane , a Twist. The Saito is the stronger of the 2.
The O.S .46 is a great engine , for someone who is not to mechanically inclined . but on the other hand, I`ve never had a problem with my 4 strokes either.
da Rock is right on the money about getting a tach for adjusting the 4 strokes HS needle till you get familiar with them.
I like both 2 and 4 stroke engines , and let the airframe dictate which one to use.