The most simple method is by marking the tie rod end threads right at the nut. That gives you an exact location. Inner tie rods may be slightly different though, depending on where you get them. I replaced my oem inner rods with NAPA's, and the NAPA's were slightly shorter. So I had to measure the difference and then apply it to the mark on my threads. Even so, when I got it aligned they said the toe was off by quite a lot. Also definately replace any other front end parts that are worn when you do the inners, since you have to get an alignment done any time you do front end work. You probably already know this, but new parts tend to wear out old parts even faster, and in return worn parts will wear out the new parts faster. So you definately save money on alignments by doing everything at once.