Hi have just tried to balance out my Spit - all electrics / batteries are as far forward as possible yet I still need 430gms (nearly 1lb) of lead DIRECTLY over the engine to balance the plane (os 91fs installed) The total weight is a shade over 4.7k or 10lbs including the lead. Does this seem excessive / will reduce the performance markedly? Thanks for your help and advice. Graham

Yes, according to the TF wieght recommendations that's a bit heavy. Mine came in bit heavier. It will fly at this wieght, but performance may not be what you like.
Try putting the flight pack battery in the engine area some where. That may reduce the amount of lead needed up front. It's worth a try, just seal the battery up well.
The TF Spit will be a bit tail heavy. One has to watch every gram to the rear. I didn't and mine has about the same amount of wieght added to the nose.