Why would converting to TD make it tail heavy? Did you add a HUGE tail-wheel? Moving the mains forward seems like it would give more nose weight. Check your balance again, 6 1/2 oz seems like a lot. It will fly, but if you could avoid adding almost half a pound, I would try.

You can add as much weight as you want, but you sacrifice a lot in the process....up to the point that it uses all of the runway to take-off or will simply not fly. Lighter planes fly better...period.

Good luck!!