This would have been in the instructions. Look at the top of the cast part of the diff. There is usually a seam or part of the casting that needs to be knocked down with a flap wheel so the arcs in the ends of the truss fit closer to the axle tubes themselves. That gap should go away.
Thank you. I mocked the truss up last thing this evening. I haven’t burned it in yet.
I’ll hit it with a flap disc when I get back to it.