With all due respect for previously submitted opinions, I submit that cured epoxy does not soften under a heat gun, and cured epoxy will not be affected by acetone at all. Having worked with this stuff (epoxy, polyester, vinylester resins) for years, both small scale, (models), and large scale, (boat building), I have never heard of such a process as you describe. Acetone is an aggressive solvent, and it will clean up uncured epoxy, but once the stuff has cured....forget it; and as for a heat gun....you can make it hot, very hot, and with enough heat you may even succeed in making it burn, (not recomended)..but you will not soften it like a thermoset plastic. The only way to remove cured epoxy is to cut, or grind it away. Cured epoxy is infinitely harder than the balsa, or plywood to which it is bonded. It will be the wood that will be much more abused by the application of heat and chemicals. Without actually seeing the weights and how and where they are attached, my guess would be to use a hacksaw blade or jewelers saw to cut them away as carefully as possible. Perhaps a Dremel tool may help. The firewall will most certainly be abraded somewhat in this, but carefully done, the plane will survive the operation.