I put a 1" shank ball on the other head and gave that a shot. It does seem to provide more room if not at an angle, and the ball has a shorter shank, allowing more range of motion vs the other ball. Now the only obvious binding when flat is the extension for the sway control.

Other side:

You can see the 90 degree chalk line on the ground under the head.
I didn't get any shank spacers with that cast head (with the higher ball mount) and my understanding is the 3 piece welded ones are more desirable anyway.
So it seems like my best bet is to go for the 1" extended ball with 1 1/4" shank with the 3 piece head. The ball shank will likely need to be cut down so there are just a couple of threads past the nut when torqued down.
I have only found "bare steel" extended balls, so I assume that it will need to be painted to protect it from becoming a rusty mess.
Once I have all that stuff the weight distribution will need to be set up from scratch. I've read that you should set up the weight distribution without the dual cam and then install the dual cam kit. Then you have to do it all over again. Doesn't it make sense at this point to set up the WD with the dual cam setup and not even try without?