Mike, you're a lot farther along than I am. Shown here is my rear former for the bifurcated pipe. Apparently my pipe is a lot longer than yours is. (I hate the way that sounds). My engine will sit almost between the main gears. There are advantages and disadvantages. The upside is my thrust tube bellmouth has plenty of vertical clearance, so no flat spot needed. The downside is fuel tank location. I also have a 2nd former with one hole that supports the tube forward of the split. Are you putting any heat reflecting material inside?