BTW came over last night for a few hours of work. He brought with him a set of four brackets he had fabricated earlier. The brackets are designed to allow for precision vertical alignment of the rails on the frame.
After a few hours of measuring, hammering, and welding, here's how things look:
Here are the brackets that Bo welded onto the rails.
Good stuff! There's a bit of welding left to do, but I have every expectation that this will be complete before the end of the night. Awesome work Bo!