Most if not all known electric water pumps simply don't deliver enough flow. A stock 375-bhp 351-C takes a minimum of 50 cubic ft/min of coolant flow to stay cool and I don't know of any electrics that pump that much. Most are around 30-35 cfm- good for dyno tests and drag racing but not road work. A large aluminum radiator will help by noticeably increasing water flow.
If you drive slowly and sedately- like around town, an electric pump will work, but on the open road where a Pantera excels, the engine will get hotter and hotter, until you're forced to slow down. And if you have a modified engine, the overheating happens quicker. On a 150 mile trip to another city, one e-pump user could not exceed a steady 70 mph. And his e-pump needed firewall mods to fit. If you're driving in a pack of friends, they will get tired of waiting for you.
A stock iron pump weighs 16 lbs while an aluminum aftermarket one that pumps the same volume weighs 8 lbs. The stock cast iron pump pulley weighs 3 lbs while an aluminum one weighs less than a pound. Pulleys are easy to make on a small lathe, in any ratio you like to tune pump cavitation out.