An update... a week later.
I've put into my routine several of the stretches mentioned in this thread, as well as the ones sent to me by Chop. One of the critical points made by Typhoon was the dropping of the knee toward the floor while stretching the calves, as to shift the tension off of the upper calf, and focus (much) more heavily on the lower calf/ankle area. (Though I am keeping straight leg calf stretch in there as well, to make sure that the upper part is properly loosened). I've also been devoting a good bit more attention to the post-workout stretching.
Been on the ankle four times since the initial post, Tues, Thurs, Sat, and earlier today. So far speed has shifted to a 9:30 pace as of today, still holding 20:00 time. Pain is still there, but only toward the end of the run and is less than before, and the swelling is significantly reduced. Overall, things feel much better, and endurance is improved (not a rigorously scientific note, but worth mentioning). I used ibuprofen last Tues/Thurs, but as of Saturday, it has not been required to control the swelling (it usually goes away within half an hour).
Current plan is to move forward at 5-10% increase in speed per week, and to maintain the same time (scheduling slots for the treadmill at the gym works well for a 20 min run).
Thanks to all for your help.