What about drilling a hole through part 2, part 1 and the other part 2. Tap a thread on the first part 2, Tap a reverse (left handed) thread on the other part 2, get a rod and thread the ends to match (one right handed, the other left handed. Stick a hex head or a screwdriver slot in the end of the rod.
That way as you rotate (tighten) the rod the two part "2"'s will move towards part 1.
You could have two locating pins on part 1 and matching holes in the part 2's to stop it flopping about.