Hi friends from RCUniverse, need some help!

I have bought and brought to life an old Viper (honestly don't even know the manufacturer) which is around 1.8m (71") wigspan and a bit shorter on the length. It use to have a RAM 750 on it. At this point in time I'm putting a K80 but will probably change to a K100.

The question is: The Elevator uses 2 servos and the space available for the servo installation is not enought for a regular servo ?(like the JR 8411 which I bought for this plane). I was told that I should use those Slim wing servos, and here comes the trouble: What is really the torque needed in this situation?

The slim servo, JR DS390 has a 75 Oz/Inch @ 6.0V and the 8411 has 188 Oz/Inch. Since itgoes one per command surface, do I really nee a 188 Oz/Inch torque servo in a plane this size? If that's true, what servo would fit this scenario? Mz Yaw is the same. No space for a standard servo to fit...

Thank you very much in advance! Great flying!<br type="_moz" />