I decided to use turnbuckles.  They are all accessible from behind the seats.

For the rudder cable fairleads, I did not have 1/8" plastic, so I modified the 1/4" UHMPE I had on hand with a router.  

Once everything was installed, I had a problem operating the elevator.  Cable tension would become very high when pulling up the elevator.  At first, I suspected that the horns were not made to specs and found that the lower one was not correct.  I made a new one, but that did not resolve the problem.  I then found the real cause...  the lower shackle at the base of the control yoke did not have enough clearance (see picture).  This was easily corrected by removing material from the yoke assembly. 

Sealing the firewall slots for the rudder pushrods.  I used rear leather as this does not burn too much.  Vinyl in comparison burns real fast and emit a big cloud of black smoke.