The ZF has a centering mechanism. So does the shifter. Removing one is supposed to free up the shifter making it shift easier. Since you only need one mechanism, it doesn't hurt to remove it.
Here's a how-to article: http://www.panteraplace.com/page76.htm
The shifter detent removal is at the top of the article.
PANTERA INTERNATIONAL
A DE TOMASO CAR CLUB
Presents the De Tomaso Forums
The On-Line Meeting Place for De Tomaso Owners and Enthusiasts From Around the World
Clicking on the banner will take you to the sponsor's website.