I'm about 10 yrs older than your coach ... we hit that 24 hr thing at its inception we did in 1/72 I think and we had guys in his range or a bit faster. The running 'boom' was well under way by early 80s - soo . 'Character building' I doubt. I was thinking if we kept it at 20m rather than 24hr - we may have peeked at character stuff. Knowing our guys tho we would have picked the pace up, perhaps ending up where we did w/ 24hr. Hindsight ...
We had wanted to 'break' the WR set by some guys in England I think. We ended up 3rd on 'all-time' world list - just behind the USA Oly guys.
I'm betting the 24hr relay was more 'visible' in the running groupee types when your coach ran. It did get get some exposure in RW - and that tended to fuel all kinds of crazy stuff. RW, at the time, was a well respected (and relatively new) mag. A nice complement to t&fn. Ideas tended to move about through word of mouth and those two mags then.
The European(Igloi-Tabori)/Lydiard-Cerutty/Australia (Clarke)/Britain and even US (Lindgren-an emerging Bowerman) elements were being test-driven by many. If memory serves there was a bit of 'not so friendly' competition for disciples. And there were 'anti-training' camps too. Pretty strong personalities and opinions. I'm not sure however if any of those mentioned would do the 24 hr thing - they did, however have their own brand of 'character building' workouts.
I worked out with Tabori for a ~summer. His workouts were legendary, and for a reason. He used to determine a 'character building ' workout by the following 'data'. After a workout, during our visible death looks, he would ask "You peece blood? Not a hard workout unless you "peece blood." I never had a hard workout with him, but I did have the death look.
And one thing he did develop - you learned you almost always had more in you than you thought. I had a teammate who trained with him for a number of years - his stories about Tabori were something to listen to. Maybe he would have liked that 24 hr - but it would have had to pass the 'peece' test.
Well that's my 24hr ... response