I was doing a torso swap, and the new upper was just way too loose on the lower. I've had to do a bunch of plumbing work around the house over the past month, so I have a lot of Teflon tape (I've been plumbing water and propane, so I needed different grades). I grabbed a roll of the heavy-duty stuff I have and gave the torso post several wraps. The tape was taller than the post, so I cut off the excess and flattened it. I then pieced the two halves of the upper torso around the post and presto, tight fit with full motion.

Just a quick tip I thought I'd put out there for anyone interested.