Sam,
The tether wiil be much easier to connect if you get rid of those diaphrames, use the close couplers on the back ends of the A units and they will look fine without them.
Also one end, the female I believe does not pull out. Don't force it as the tethers are anchored into the shell by two plastic pins that lock the tether to the shell. if they become dislodged from the shell they don't go back in very easy even taking off the shell does not help.
Good luck with your engines, if you use the B unit put the close couplers on them instead of the A units. They pull like nobody's business, sound good to.
The last time I used mine was the easiest with the tethers, maybe they loosen up with use. To undo the tether you squeeze in the sides. They come apart surprising easy.
JohnB