Same as -2 I think. There should be a plug on the driver's side (it has a big allen "head") below and in front of the shifter box. Technically mine has a factory dipstick inserted there on my very early pushbutton car, though those are very rare. But basically that's the fill level from everything I've ever heard. Both my -1s had the same hole there. I think you can also fill there, as my first -1 didn't have the top fill, though the top fill hole is probably easier.
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.