Bonjour Jim,
My experience is based on a Yarrow boiler I bought :
A small boiler is quite difficult to manage because the fire remains atscale 1 and I think your one is quite larger than mine.
If you are able to create the heat, it is not stable, it rises very high and falls very quickly. This means that the brazing must be perfect and made with a more resistant material than the classic silver mixtures used on our gas boilers.
Brass does not like strong variations in heat, stainless steel is very difficult to work with, copper remains the metal suited to our scale.
Besides this, I have very skilled friends who have been able to install such a boiler in a launch, example :