crane does not recommend the use of this kit with springs that have more than 330 lbs, I've used this kit with a 120-320 lbs springs with no problem, but I had to take them of and machine the heads for guideplates and tap 7/16 screw in studs when I used HR cam with the same spring presure as your's, don't risk it.
good luck
Hani
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.