I have 2 4*s 40 size with 4 strokes one has a Mag 61 the other has a OS 52 . The 61 is almost able to go vertical it might with another prop combination .I am using a master air screw 13x8 on it. That planes weight is 4lbs 12oz. The one with the OS is slightly heaver because of wheel pants and a full length wing the other is cut one bayeach side.It is not quite as spirited. These engines are not as powerful as that 70 will be but they weight 5 0z less you will probably have to add some weight to the tail . I have a 60 size ready to cover with the engine size undecided . In my opinion the 70 a little much for the 40 but a little small for the 60 .