Wait, what? Are you mixing up Ford E350 with Mercedes E350? As per his signature (albeit not visible on mobile) it's a Ford Econoline E350Absolutely NOT! That stuff blocks coolant passages including those in the heater core.
OP, go to FCPEuro to buy a WP that's made by the supplier to MB.
Graf appears to be your best bet. https://www.fcpeuro.com/Mercedes~Benz-parts/300E/?year=1993&m=20&e=614&t=5&b=5&d=15505&v=&keywords=water pump
BTW, are you sure it's a 1993 MB 350? FCPEuro's website doesn't show a 350 for MY 1993.