Ted,
Well you could go back to the stock Dragonfly arrangement of a single carb!
I run a Mark 3, which has twin Amal 274 carbs, and yes it is the nature of the beast that it has heavy throttle action. It is inherent as you are pulling against two throttle slide return springs.
About all you can do are the obvious items that you likely have already thought of. That is, switch to Teflon lined cable casing. Also the plastic cable splitter box might be a bit flimsy and is binding under load, offsetting the natural lubricity of plastic construction. If you think that is it, there are plated brass versions about, as used originally. You could look for lighter springs for the throttle slides (not sure if they exist) but unless your carbs are well bedded in (that is worn out!) you will find the stock springs are required to positively shut the slides. There is nothing more exciting than rolling off the throttle and then kicking the carbs with your toe to try to get the engine to slow down! I re-sleeved my carbs and at first they tended to stick. Without an air filter, they do wear in quickly.
-Doug