Try this.
Hook up an electric fuel pump that pulls through the fuel pickup tube and dumps into the filler or the gauge sender hole.
Put a couple of gallons on new gas in it and let the thing run a couple of days.
There really isn't anything better at cleaning the inside of the tank then gas is.
Put one of your clear filters in line to the pump. Keep changing everything until it all runs clean.
I changed th tank plug type to what is used now, an Allen socket drive with o ring. It is lower profile then the original. I believe the application was Audi.
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.