Tie rod ends, what is the difference?

I'm helping a friend restore a 67 383 GTS dart. The car came with a partial new front end kit. I have two Moog ES 319R outer tie rod ends and need to order the two inner ones. We're using a 68 K-member. I noticed that 62-67 use Moog ES-319L and 68-76 uses ES-401L ? Can some one tell me what the difference is? I need to order two but not sure which ones to order.