The 340 and 318 are internally balanced, the 360 is externally balanced. I have swapped many 340s for 318s and used the transmissions, TC, and flex plate without issue as well as flywheels, etc. When you go 360, then you need an externally balanced flywheel or TC as well as the externally balanced dampner.
I have had people say not to use a 318 flex plate with a 340 stating that it wasn't strong enough; I disagree.