I think Ron Clarke and his group had the simplest training you could find. They did a good paced run for about an hour after work each day, a race and a long run at the weekend and in Ron's case, a 5-6 mile AM run.
Shorter's was also really simple. A session of longer reps once a week, a session of shorter, faster ones, usually a race or some sort of tempo runs, and a 20 or so mile run and usually a couple 10 mile runs on the other days.
Ron Hill ran back and forth from work, seven miles minimum, usually more on the run home, a couple days of intervals, either 70 second bursts or counting 10 strides, then 20, then 30, etc, up to 100 the n back down, a weekly race and a long weekend run.
Mark Nenow's training was a lot like Clarke's, a couple good paced runs a day and a lot of volume.
If you can track down any of the "How They Train" books from the 60s to 80s you'll see that a lot of people had the same plan pretty much year round and it was really simple. Check Bob Hodge's website and you'll see some really detailed samples including Bob's who once told me that many people just can't believe what a really simple sport running is.