From what I see it doesn't need to be a S curve control line. The top curve can be removed if the control rod is attached to the elevator via a ball link or link stopper placed some distance out on the elevator.
You do not have the luxury of seeing the original plans and instructions.
The orginal it had the elevator servo inside the front of the fuselage. The elevator pushrod ran straihgt back near the wing root, then entered the wing and curved sideways inside of the right wing, then curved the opposite way ( "S" ) still inside of the wing, and exiting at a shallow angle from the airfoil near the top of the wing (parallel to the wing bottom) to go straight back inside the boom , and then the curve "UP" along the right rudder to connect to the elevator. So actually originally it was three curves, an entire "S" horizontally and then a shallow curve up. That played absolute hell with trying to get a smooth free-sliding pushrod as is necessary to avoid having problems with hysterysis.
So, eliminating the whole horizontal "S" curve from front fuselage to exit out the right wing for the boom, by locating the servo in the wing (or boom) is a major control system improvement. Leaving just the easier single upwards curve to deal with. Or a direct-drive servo on the stab, though that adds tailweight and with today's lighter radio gear the model needs noseweight to begin with.
Ok, I misread the instructions. I used epoxy instead of crimping, and now my couplers won't crimp to the cable.......because of the epoxy (?). And I don't want to exert too much pressure while crimping, for fear that I might cut the coupler/cable.
I feel very confident that the epoxy will hold.
Well, I would not trust crimping alone anyway (If I crimped, I'd put thick CA in it then crimp before it cured. Or if crimped dry, carefully apply thin CA and use accelerator before it could seep towards the pushrod sleeving). What I often do with that .030 Sullivan cable and threaded brass coupler is to solder the coupler to the cable. Using some good flux, and making sure not to get the threads messed up. But that has to be done first, can't do that with the pushrod installed as the heat would melt the pushrod sleeving and a slip of the soldering iron could damage other things close by. The epoxy probably will hold OK. You have not tried to crimp after the epoxy cured, right? If you did, then you might fracture the epoxy, or break the bond, and then it could slip. Sometimes when I do not use solder to bond the cable to the sleeve, I use thick CA, being careful to be sure to spray accelerator on the cable side of the coupler to be sure no CA ends to getting into the sleeving.
Do remember, nobody ever makes mistakes while building. The model I showed photos of, there is absolutely no 3/16" burn/melt hole near about an inch or so back from the tip of the fuselage nose, from a momentarily misplaced soldering iron. Nope, nope, nope.....
Key thing is to catch the potential flight safety/control/structural issues and fix before flight. Seems like you are OK.
Another bit of advice, I think I mentioned it earlier. When you are done and close to flight, do a lateral balance test to find out which side is heavier. Which on this model should be the side that has the servo and pushrod, the "heavier" side will have the wingtip dipped down from level, lighter wing higher up. Then add some weight to the wingtip on the other side (the high one), until it balances out evenly (horizontally). I usually use solder for the weight. Now, this is not actually a tip specifically for this model so much as a universal tip for all R/C models fabricated in a manner where both wings are not likely to weigh exactly the same (like built-up wings or vac-bagged composite wings), or there is some asymmetrical fabrication such as in this case the servo, pushrod, and even electrical wring running on one side but not the other. But this model definitely is going have one side heavier than the other and require it.
I do not recall if the original instructions mentioned that. It should have. Even with the servo in the fuselage, the mass of the "S"-ing pushrod system and patching back over the nasty "S" trench left on the top of the wing skin to provide access for the pushrod sleeving. And the fact that the home-skinned (weighted, or pressed, or vac-bagged) wing panels were not likely to turn out of equal mass.