What I did is this...
Take #41 Clone & Bacara...
Take off Bacara's head, and cut the ball off his neckpost perfectly. Cut the ball off the #41's neckpost as well. Take plastic welder (Plast-Struct) and weld the Bacara Neckball onto the #41 body, let it cure overnight at least. Paint any possible white showing with just a dab of flat black, very simple...
Pop on Bacara's head.
The problem I ran into more was getting Bac's shoulder pad onto the #41 body. I tried stretching it after a boil but it was gonna tear I think. I wound up cutting a groove into the figure's back and under his armpits that fit the straps of the shoulder/chest pad into it perfectly, and allowed the accessory to fit the figure perfectly. A way to avoid this would've likely been using the #6 Clone (Quick Draw) as opposed to teh SA figure. It has a smaller "backpack" piece to it and is generally thinner built I think. Changing neckballs would've been the same procedure (if you needed to change it at all?).
I also swapped out the left hands of Bacara and the #41. The Bacara hand is cool and unique, and good for "calling troops forward".