I also face same problem before.
I bought a hop-up mount but it can't fit exiting servo.
Two way I could choice, 1. forget the new mount 2. buy a new servo that fit the new mount.
However, another issues was found - connector size and torque.
Normally, I can select 9g servo but it seems that connector size is difference and torque
is not enough. Finally, I give it up.