I ran across these drain valves at a local boat store.  Also on ebay.   IMHO, these are pretty neat, all you need is a socket or box end wrench to open the valve.  Nothing to rust and no  butterfly to break or rust.  I put a couple of these on my 56 Bird.  I haven't had these on long, but should last a long time.
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54 Victoria 312;  48 Ford Conv 302, 56 Bird 312
Forever Ford
Midland Park, NJ