I did go over your build,very nice and very well thought out. I was in a high school metal shop class 1972 when I built my first and only steam engine. Having finished that one the teacher handed me the plans for this elbow engine,but I never got to start it but I kept the prints,and those are the ones I used. On to a two year trade school and then on to tool & die apprenticeship. Then Unigraphics CAD designer for the last 15 yrs.
I never had the time to build it until now-RETIRED! I so missed being out on the floor. First thing I did was build a small shop and then a Stuart beam engine. I had been sitting on those plans all that time.
I knew that the cylinders might be a problem so I made them from one piece then split and kept the reference the same. Pistons were easy bent with a pipe and trued with v-block and tenth DTI. Every thing else was ground in square.
The problem is with friction and sealing at the cly bases witch your design addressed. I will try to sell this first one-"self supporting through my own contributions" .
I have started another,just for me!
OH and the import crap is just that. Most people know what quality is,and that is what they are after, it lasts forever.
Mart