Mark has it down. I usually build them with one threaded and one unthreaded end, and the "plugs" seem to encurage that, as two have 1/16" holes and two have slightly larger holes for the threaded rod. I only need to measure the overall length within an inch or two, because I Z-bend the wire end (servo end) after the pushrods are installed in the plane, then cut off the excess.

You're correct that the hooks at the end of the wire have to be slightly shorter than the I.D. of the pushrod. Too long and you won't be able to fit it in the tube, too short and it won't go all the way through the hole you drilled. Better to bend it a little on the long side, then trim it to fit inside the tube. BE SURE, as Mark stated, to slip the plug on the wire before you bend the hook.

I try to drill the holes on either end along the same longitudinal line, and let the epoxy cure with the holes down (overhang the ends), so the epoxy fills in around the hooks (I use epoxy on the wire as well as the plug).