I'm debating making a slip-fit sleeve to hold the chamber end of the barrel, or to make an adapter that accepts the barrel threads that will reach back to my spider. Thoughts?
The purpose of the spider isn't just to keep the back end from flopping around, if you want to do that, you can wedge pieces of cardboard between the barrel and the spindles bore to do that. The purpose of the adjustable spider is to aid in the precise alignment of the working end of the bore. On short barrels, I use a split nylon bushing which is tapered, that slips over and runs up the taper of the barrel, which beats the hell out of looking for just the right piece of cardboard. And because it is split, I can adjust the fit in the spindle bore by running it further up the barrels taper. Pretty cool actually.
As far as the correct torque goes, it's hard to put a number to it. Over time you develop a feel for how tight to torque them. Each one has their own feel. I use to apply enough torque to where my eye's would begin to cloud, but now, many years and barrels later, I use the "work bench off the floor" method. Don't use loctite!