Picked up two 6" x 4" stove pipe reducers and a 4" X 3" and 24" of 3" pipe. I disassembled a 6" X 4" and the 4" X 3" reducers, welded the angled collars together and discovered that the 6" end would snap right into a groove inside the top of the 6" insulated chimney pipe. Things don't usually work that way for me. If I had planned it there would be no way it would have fit like that! Then slipped the other 6" X 4" reducer in the bottom end. This is where the burner will be and the 4" section will make a nice spot to position it. This reducer is removable so the coil will be slid in from the bottom. When it sits in the bracket (my next project) and is clamped in place everything will be secure. I sanded down the shiny stainless and painted the ends with header paint and the body with regular satin black. The outside of the insulated pipe doesn't need high-heat paint. I'll probably welded a piece of angle iron vertically between the stays to provide a rack upon which to secure two brass straps for the boiler and the assorted hardware that will be plumbed to it.
I mocked it up a little to get an idea of how it might look. I'll be using a different headlight and seat, something in brown leather with copper rivets probably. The boiler sticks out from the side about 12". The stack will get shortened a good bit. I'll be building a wood and brass box for the other side to balance it some. It will contain a motorcycle battery, high pressure water pump and the electrical stuff, perhaps a 12v-110v inverter to power a steam solenoid to serve as the power valve on the head. Maybe.
Cool low profile tires are for racing purposes.