I tried making a jig a while back but found that I couldn't make it accurate enough. It would probably have to be machined, and then you would need one for each kind of loco too.
I install the stanchions by eyeballing them against the vertical lines on the body of the loco. It's usually possible to adjust them with the tip of a tweezers, and they can even be bent a little bit after the CA sets up. No much magic to it, just good light, some magnification, and make sure you're looking at each one square on. I first sight them from the side, then from the ends to line them up, and then also from the top, repeating as necessary.
I prefer to install the longer stanchions from the GMM fret, and them trim them after the PB wire is soldered. That allows me to make adjustments if needed, and it avoids the balancing act of trying to solder onto the very end of each stanchion. It also compensates if any of the holes drilled for the stanchions are not perfectly aligned. I've heard that some guys wrap the flat ends of the stanchions around the PB wire, but I've never tried that myself.
Some handrails have angled and/or compound bends. Sometimes it helps to make a template on paper, but I don't think it's necessary to have all the bends precisely right relative to the prototype. As long as the square angles are pretty square, and parallel lines remain parallel, it should look pretty good when finished.
The first few times will take some extra patience, but I think that other than melting the shell with the soldering iron, there aren't too many mistakes that can't be corrected.
Ed
