I'm assuming you want to use the torso of one with the arms of the ROTJ version?
I'm not sure what the point of the parts swapping is?
Is it to get the paint scheme changed? If so why not just repaint the figure?
I really thing the ESB figure is the better version of boba, but if your wanting to use that figure to make the ROTJ style paint scheme then I would just swap the belt and jet-pack and repaint the gauntlets the correct red color.
If you are still hell bent on swapping the arms then I would crack the torsos of both figures and just swap them out at the shoulders, that'd be the easiest method.
It'd be easier to give you help if I knew better what the end purpose was...