I take a bunch of pennies and see how much weight I am needing by adding them a few at a time.

As daRock said, the conversion shouldn't shift much weight towards the nose. You're removing a large nose wheel and adding a tiny wheel way out on the tail. Before you add anything try moving the battery and receiver back. Anymore you won't gain much with the receiver . . . but it all helps.

Sheet lead between the tailwheel bracket and the fuselage is a good spot. The further back the less you'll need. And lighter always flies better.