replacing the throttle arm with an eccentric wheel should do fine for your arrangement.
thinking...the eccentric wheel is basicaly a reducing radius arm so why not use multiple arms of varing lenght. I would think just one long arm would give you what you want.
if you can add some info like
total throttle cable travel
butter fly total travel angle
how much reduction of opening in the bottom end
open angle at which to increase opening rate
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.