You have the right idea - an adjustable drag link is what you need in order to correctly center the steering wheel and, when centered with the drag link properly adjusted, the number of turns of the steering wheel in either direction will be the same - stop to stop. In addition, the steering wheel will be centered, or very close, half way through the entire run - stop to stop.
There are three ways to approach this chore.
You can go with two female tierod ends and make a rod threaded on each end the proper length to work for your application. One end of the rod will have to be threaded with a left hand thread. That usually stops most unless you can resource a way to get a left hand thread made for you. Another thing you can do, and probably the easiest, is get a tie rod, cut the center of it out and weld it together at the proper length so you have a "short" tie rod which will now be your drag link. Finally, you can use the drag link you have and grind the "keys" out of the pitman arm so that it will go onto the steering box shaft (pitman shaft) at any position you want it to go on the shaft. With that approach, you can set the pitman arm in the proper spot to center up the steering box and the steering wheel.
I don't care for or endorse the last idea, but it can be done.
Every steering box is a little different and through experience with the front ends on Chevy trucks, I have found that if you want it set up the way it should be, and from your post I see you do, the best way is to make it the way you need it to work for you and do what you want it to do.
A good source for tie rod ends is ebaY. They are on their quite a bit. Another place is your FLAPS.
Joe
