I found an interview with Vyachesku Makarovich Boras coach.
He states that in base prep they would get up to 450k’s a month roughly 280 miles.
So probably somewhere between 50 and 60 miles a week give or take. Y.B. liked to do long runs of 20k but sometimes he would even go as much as 30k. He is not considered a high volume runner, as he is also stricly an 800 specialist. Never the less his base training still far exceeds that of 30 miles a week. This interview was from 2001 I’m not sure how much if any his training has changed since 2001.