It also has a ruddy great crankshaft which dwarfs the T-Bird's. Check out the service manuals to compare. Both the balancer shaft and crankshaft span the length of the R3 engine.
Bit extreme, but good to see you found a solution.
The T'bird should never be seen as a competitor to the Rocket. Only reasonable comparison should be to Dynas and Softails and the naked VN1700. In that company it wins hands down.