I always hang anything that I am painting, and hit all sides at once...there are times when my backyard had stuff hanging from every low branch and stretched across the hammock stand, but it works!
Would brazing rods work for the boiler? Usually you can use a propane torch and this will give you a higher melting point.
I did have the parts hanging up the second time I painted them but I really don't have any good places to paint so they are usually poorly lit, dusty or require the part to be moved somewhere. I really would like to build my own small paint booth in the garage one of these days.
Brazing rods might work. Do you know if they work with brass? The parts I have to connect are the steam line from a brass nut that screws to the boiler and I also need to connect the steam lines to the engine.