The midsection is, for the most part, merely the extention of the emitter.  For example, in the above picture, the center pieces extending from the emitter to the motor cycle handle is all one piece (the solid 3/4 aluminum round tube.)  The other peices are actually spare parts I had from a failed Graflex replica.
 
 

Parts:

 

From left to right, the parts are:
 

• 7/8 inch piece of copper tubing, cut down to .3 inches.
• A brass washer that comes in the same "assorted washer" set you get for the motorcycle handle.
• A spare peice of chrome tubing cut down to .3 inches.

Really, you could make this out of what ever material you want or find lying around the house, since you will eventually paint it over with black, anyway.

Notice the groove near the emitter section.  This is one of the reasons you want for the 3/4 inch peice to be solid!   I carved this out with a triangular shaped file, being very careful my unsteady hand did not wander.  I'm sure you can imagine many ways in which to shape this groove, but if you have lots of patients, this will do just fine.  Draw a straight line on the aluminum before you start grinding, then take it slow and steady.