Just to chime in,
On my recent rebuild of a 216, we replaced that drain-cock with a brass quarter-turn valve, (not sure what they're called, I call them "gas-style", 'cause you see them on gas lines sometimes). I hate the above-linked pet-cocks, even if they ARE original: I find them hard to use, I think they fail far too easily, and are prone to breaking off. Just my opinion, anyway.
During our install, we had to drain the coolant twice chasing down thermostat issues. We ran about a one-foot line from that valve, down past all the engine stuff. Now, when we need to drain the coolant, it's a simple matter of sticking a clean bucket under the drain-hose, opening the valve, and presto.
I know you're a stickler for originality, and good-on-ya' for it; but I know you drive that beautiful truck a lot, so I thought I'd offer this idea up. Let me know if you want pics, and I'll get some this week.
-Michael
