The problem as I see it is NOT engine weight, its simple engine torque! Secondarily, the dimensions of some engine's heads can run into stiffening tubes. Which on a 'Goose, is about all you got back there, so cutting or relocating any tubes seriously compromises the structure. As for stiffening up the existing structure, I'm gonna defer to Steve Liebenow, 'Goose owner, who IMHO has done about everything to his '69 with a Boss 302 installed, that one can do to a Mangusta.
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.