I can only comment on the Weiand pump that has been satisfactory on my '72L for 13 years now. In my opinion, an aluminum 351-C water pump should have a back-plate on the impeller and a port for the warm-up bypass, just in case you live in a real cold climate and want to warm up faster. The Weiand waterpump has neither although I added a stainless backplate for a little more water flow. Weiand also has a thin heater-hose boss that can (and will!) crack if a fitting is overtightened in it.It is fairly cheap, rebuildable and widely used as-is in the Pantera community, though.
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.