Transitioning from HIM to a 10K

I just finished my first Half Ironman on Sunday for which I pretty much followed Matt Fitzgerald's Level 2 plan outlined in Triathlete Magazine's Essential Week-by-Week Training Guide. Finishing the HIM was my big goal this year, but now I'd like to shift gears a bit to two secondary goals I have which is running a sub 20 5K and doing a Sub 7 minute pace for a 10K.

Right now, I'm taking this week off and will ease back into training next week. The 5K I'm targeting is October 30th and the 10K is Nov 26. I've done these races numerous times and the PRs are 21:30 and 44:53. My tentative plan is to use Hal Higdon's Intermediate 10K plan (http://www.halhigdon.com/10ktraining/10kinter.htm) once I am 8 weeks out, but I know many of you guys don't think speed work is good unless you are already putting in major running mileage (which I haven't). So I was just wondering if you had any suggestions on modifying Hal's plan (or something different) than I could do to accomplish my goals?

Thanks!