Welded a piece of angle iron vertically between the chain stay and the former gas-tank-behind-the-seat-bracket. That previously discarded part of the project has now come in handy. I'll have to make a rack out of it and it may be useful as a place to mount some steam hardware. Welded the boiler support ring to the angle iron and added a support rod. The angle iron meets the ring at a right angle because there will be two brass straps on the boiler that need a flat vertical place to bolt into. I mounted the boiler slightly higher than was shown in the mock-up photos in order to keep it out of the way of the rear axle/nut.