According to Chuck Melton's site the first L was around chassis # 4269. With DeTomaso's penchant for precise record keeping I doubt anyone can know for sure.
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.