Thanks for all the info. I took a closer look and it does appear to be a real plug, but with an Allen wrench socket instead of a slot. However, it's still plastic and I managed to round off the corners, so I'm going to try disconnecting the supply hose to he heater, catching what is pumped out.

Thanks for the reply, Mark. Were it only that simple, but the replacement radiator, at the very bottom, has a hex nut shape in the plastic molding which doesn't appear to be removable. I've been fooled before, but I'm not quite ready to put a wrench on it just yet. I'm hoping there's a simple...

I'm new to the LR universe, having recently purchased a 2002 P38 fixer-upper. At the moment I'm attempting to drain the old coolant, but discovered that the replacement radiator, which has plastic headers, has no drain plug in the bottom. Any suggestions on alternative approach?