Karl,
I'm surprised you know Derek - I thought you were British.
Yes, you are correct about all the muscles he would have used around his farm.
Jack Foster was another, although not a farmer, did most of his running off-road, running lots of hills and jumping fences.
Just think we all come in different packages.
Bill Ballie - very stocky, a completely different style to Jeff Julian who was a great x-country and marathon man. Of Arthur's boys Barry Magee looked like the ballet dancer - beautiful style, just ran effortlessly. But I don't think Lydiard worried to much about style, he had a very good woman runner who used to kick her legs out to the side - she was also a great x-country and marathon runner - he never tried to change her style.
Yes, I'm running Christchurch. I've never run it before, only running it 'cause I missed Rotorua as I was in the Gold Coast with my family.
Arthur loved hills for strength training, thought the most important muscles were your quads.