Early cars had the battery in the right side of the engine compartment over the rocker panel extension.
Probably the best place for it is in a drop down box from the front trunk.
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.