danny if i am not mistaken that will need modification also ,the HS-56 is the direct drop in with the hitec servo saver from associated
i did the hs-81 mod to mine and all i did was used the stock servo saver pc that slides over the horn and drilled it out to fit over top of the splines ,but dont drill it too far or it will just slop all around .
then i just used DBL sided servo tape and cleaned the chassis and servo case real good and stuck'er fast and been holding since
not hard to do honestly
but the 56 is a direct replacement with the saver