Rather than send the pictures direct to Chuck, it might be a bit more informative if I show them here, just to show how easy a vertical boiler build can be assembled.
This is a commercial vertical boiler built by Cheddar and it is well over 20 years old and has had much over 1,000 hours steaming on it.
Sorry the writing is so small, I couldn't get it to adjust the size in my basic paint program
It utilizes four flanged plates, 16 x 3/8" firetubes and a boiler tube in it's main make-up.
This is showing where I have removed the safety valve, steam take off pipe and taken out the four self tappers that hold the end flanges on.
The ceramic gas burner is screwed onto the bottom flange to hold it in the correct position.
This shot shows the straight thru make-up of the boiler tubes.
As Jason stated about gas burning clean, this boiler has NEVER been cleaned out in the burn area during the whole of it's working life.
This is the top collection area at the top of the boiler showing the two take off's. One for the safety valve, the other for the steam to engine.
They each stand up from the top soldered in plate by about 1", so making the position of that soldered in one about 3/4" from the top, as they protrude from the top loose fitting flange plate by about 1/8".
The burner soldered in plate is 1 3/8" in from the boiler tube end.
Only four entry points into the boiler on the side. The left hand one is for a gauge, the middle is if you want to fit a clack valve for feeding in water and on the right, the two water gauge fittings.
I have made many boilers to this design from 2" diameter upwards to 4", and all have steamed very freely. This one went from full cold to ready to power the engine (45 psi on gauge) between 4 and 5 minutes, depending on how cold the weather was.
I hope this had made things a little clearer.
John