BR - my understanding of Lydiard's ideas:
1. He talks of doing up to 100 miles per week at 'best aerobic pace' - supplemented with as much easy jogging as you can manage. Like all great coaches, he is fairly dogmatic - 'Nobody can do more than 100 miles a week at this effort, etc...)' Then again, most of us aren't going to try to prove him wrong ;o)
2. Lydiard's runners did a lot of their aerobic work on hilly terrain (roads). Just at their steady state, not surging / jogging. I have not seen Lydiard talk about HRs - more about perceived effort (like comments from Pantman & myself earlier in this thread).
Personally, I will only be using my HRM to control my slower runs. If your HR goes above your ideal training rate from time to time, that is not a problem, so long as over the course of the run you are not building up lactic acid.