A paced Moorcroft on that day would have been able to run 12.56-58. Moorcroft's training was not particularly unusual or different to his contempories.
He was the fastest 1500m runner to really have a red hot crack at the 5000m world record. Faster 1500m runner Said Aouita was able to lower it further to 12.58.
Mottram was a more talented distance runner than Moorcroft. He also was a 100% full time professional who probably covered those "one percenters" a bit better. He wasn't as talented as Aouita. Aouita's training program was crap. Had he trained like Moorcroft or Mottram he would have been able to run sub 12.50.
Clarke was not as talented at the mid-distances as Mottram. His best mile was just 4.00, perhaps worth 3.56-57 on today's tracks. He was never going to run comparitvely as fast as Mottram (3.48)(or Moorcroft (3.49)) over 5k.
His best time would perhaps be worth just 13.05 on today's tracks. He was a superior 10000m runner to Mottram though. Mottram's best was 27.34, Clarke ran 27.39 on a poor quality cinder track, having to run well away from the inside most of the way because of track deterioration. This was probably worth a 27.10-15 on today's tracks, this was run solo. Clarke felt it was his second best 10000m race.
Clarke was an amateur who worked. Travel to Europe from Australia was slow in those days. He would race frequently to make the trips worth his while.
Clarke didn't have access to the benefits of a professional athletes lifestyle. The small details that can make quite a difference to performance. His approach to training wasn't as refined as the modern day athletes.
He basically ran lots of mileage, often as progressive tempo type runs. A lot of this was on the turf of Caulfield racecourse and a lot was on the hilly roads (mostly dirt) and trails of the Dandenongs. He raced very frequently, at any distance that was available. He didn't do a great deal of interval type work because he raced so often.
He also did what we now call core work and other strength training. Not surprising as his big bro. was a champion Australian footballer.
Was his training ideal? Probably not. I wonder what Renato would have been able to do with a guy like Ron if he had him as a full time pro runner?