There are tools called a torque multipliers. You can find them on the internet. They don't appear to be cheap. You might be able to find a used one cheap on ebay, but then can you trust its accuracy? You might also be able to rent one somewhere?
Art
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.