Where...as far forward as possible (in the cowling). How...lead shot mixed with epoxy and spooned into the cowl or wherever it is to go. Put the shot into a container, such as 35MM film comes in, until you get the right amount to achieve the correct CG. Then mix in the epoxy and put it all in the area you have chosen. Sure beats trying to melt lead into the form needed to get the balance you want. Last, does not affect the receiver. Regards.