I have an airplane with dual servos for the elevator. JR 8103 TX. Linkages are all idential. I've set up the radio with the correct end points, subtrim, trav adj. etc.
The elevator halves still do not perfectly match. They are fine transitioning from up and down, however they tend to go a little astray when nearing the travel limit on high rates. I heard a matchbox will fix this problem, however, I see no good articles on the basics of how it works. Please advise.

How are you running the servos, are they on a "Y" or mixed in the radio? What do you mean by correct end points, and astray?

Matchbox has the same basic controls that you would have in a radio, i.e. normal/reverse, endpoint and subtrim. If you are using 2 channels to drive your elevator servos and can't fix the problem via the radio, a matchbox won't help. If you are using a “Y”, the match box may help, depending upon what you mean by “astray.” It will not fix an differential movement issue between surfaces that is often seen when servo pots aren’t equal or the linkage geometry is not identical .

A match box was released to help people to synchronize two servos using one single channel; you may control the range of move and the direction it moves. Since the appearance of the computerized radios with 8 plus channels, this match box was almost useless since you can program all the stuff from you transmitter, by example, making work two elevator halves with two servos was a nightmare if you do not have a match box or o computerized radio. If you already own a computerized radio (My JR 8103 works flawlessly) you can set up the mixing for a a dual elevator servos, sometimes one of them will not travel the same as the other but there is more in those radios, like travel adjust and sub trim which will help you to set it up with out the use of a match box.
In the other hand, the match box is of a great help if you are running out of channels in your radio.