Part #84 was placed toward the left. The wire connector is on the right, with the square bolt. Part 84 is held down with either a rivet or allen head bolt.
The motor coil part was placed on the Han Hoth and Bespin blaster (shoot vader). I think it was flipped around on the Bespin version, so that "Motor" is facing the trigger and "coil" is facing the hammer.
If you're making the Bespin version, I wouldn't worry about the piston halves. Just leave them off.
I've seen some good photos of the Bespin version (People Magazine) and I didn't see any residue or marks left from the piston halves.
There was a theory floating around for a while that piston halves were glued on to the side of the Luke blaster while filming the Degobah scenes. Those piston halves were glued on vertically. In fact, this can be seen on the stunt version....which in my opion, sucks. It just isn't much to look at. :/
Any way, those piston halves fell off once the prop was holstered. It's one reason why they were left off for the rest of the film (Bespin scenes).