i have put a .61 TT engine 2 stroke on and this engine seems really heavy - if i place the 6v rx battery on the tail fin that'l just about balance it - is it ok to pad the battery and is the tail strong enough to hold the battery inside?

i reinforced the firewall with another layer of ply and larger captive nuts on the 60 sized engine mount- cowl just abut fits -

the plane seems quite heavy now with a 61 on it ?? wil the greater power compensate for the increase in weight too?