Without knowing anything else...or when I just don't know anything else...I like to turn the shaft on the steering box all the way over one way to the stop (by hand), then turn it all the way the other direction while counting rotations to it's stop, then go halfway back. Then hook up the steering wheel centered. Really you should consider the angle of the pittman arm vs. the rest of the linkage also, but this will get you by. Once the steering box is centered thusly, your tie rod lengths should also be the same, when the wheels are pointed straight...if not, just kinda fudge everything a little to work it out.
Obviously if there are index marks, flat spots, skipped splines or whatever to indicate indexes on the particular components you need to include that in your considerations.