in case you aren't familiar with this and run into it; people like Og and Dick can skip as I'm sure they read my original note and said something like "You didn't know that? Dumbass."
I mentioned the overflow tank also acts as the filler location; the cap holds pressure. Take it off, open the drain cock on the bottom of the radiator and let it go. Then you have to use something like a siphon or vacuum pump to suck all the old coolant out of the tank(I used the vacuum pump I have for bleeding brakes and soaking epoxy into stuff).
When it's completely drained, close the drain, mix your coolant and water 50/50 and fill the overflow tank(is it still that, really?), then start the engine. It slowly sucked the coolant into the system, I just kept adding solution until it stopped drawing. I'll check the tank again after driving it a while and top off if needed.
Couple of notes: I checked a Ford forum looking for information when I first found no cap, which is where I found 'fill the tank and start the engine'. One guy there said his would not suck the solution in, the consensus was that his thermostat may not be working; no idea. He took his to a shop, and they stuck a vacuum hose onto one of the hoses going to the tank and sucked the coolant in that way.
Second, it occurred to me as I watched the stuff flow that you could, after things have stopped draining, start the motor for a minute so any old coolant still in the system would be pumped to the radiator to drain; if there was any, it wasn't much, so I didn't worry about it. Doing it again, I'd give it a try.