ORIGINAL: opjose
If you are talking about say a throttle servo, things may be a bit different, and you may want to make sure that the throttle servo can "give" a bit to deal with vibration.
To add a little to what OPJose has said. The throttle servo will actually have a little extra dampening from vibration because you need to use nylon pushrods with a gasser, and not metal pushrods. Metal pushrods on the throttle servo on a gasser can cause interference from the ignition system to be transferred back to the radio system which can cause a lose of the plane.
As to your original question, your original servos will do just fine with the new gas engine in the plane.
Ken