I think Hall Pantera has, or had, 180s for the 351-W. And the new Ford GT-40 doesn't run bundle-of-snakes headers; they have dual headers with cat-converters clearly visible on them. Maybe the kit-car makers that supply old-style GT-40s have them built somewhere. Not my line of expertise.
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.