Ah OK, that was really simple... I'm kind of embarrassed
I'd delete this thread but maybe some other noob will find this useful
So... being new to Playmaker and Unity I forgot that you could lock the Playmaker window and view other objects in the Inspector window. Using "Tween Vector3 Call Play" I was selecting the Target object correctly, BUT instead of dragging and dropping the Tween Component, I was using the little button next to the 'Target Component' option to open a list of Tweens for the object. Unfortunately that list only lists the first Tween on each object. Also the name of the tween is never displayed, just the object its attached too. So ya, lock button is useful