6 oz is not a a lot? It's plenty in my book; heck, it's a decent size battery pack. Double check where your CG is then figure out if you can move existing weight within the airplane to mitigate the CG problem. It's an AT-6 so you're limited by the cowl how far forward the engine can go but if you can move the engine forward withing acceptable limits, move it- it's the biggest chunk of weight out front with the biggest moment arm (forward of the CG, that is) so small movements will have a greater effect than moving stuff that is more closely located to the CG. I'm not a Warbird expert- but minimizing the wing loading is a plus on a typical warbird with high wing loading.