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Yeah I think that would be a good progression. Make each introductory run an easy one, and keep everything else the same before ramping anything up by way of either length of long run or additional tempo/race pace/interval session. IMO the key to managing a HM if your usual day-to-day training isn't very high volume is to increase the mileage rather than smashing fast reps, and I think the other plan you linked has too much intensity and not enough easy running. HH has a good balance I think.
At the moment I do three days per week. Do you think it would be possible / safe to ramp up to four for the first six weeks, then five for the last six?