Iteration #18 had a conflict issue with the top plate & the rivets of the bell crank. To clear the rivets, I simply angled the top of the brackets. The two-bolt attachment screws offset any rotation of the angle. Trial fits are good.
I am going to try Ben’s recommendation to use soft rivets to attach the Dsub shell. I understand his point that the #4-40 screws may loosen over time, so a permanent attachment is best.