Yes I think that the cardiovascular benefits could be gotten from other types of training.
Ron Clarke's training seems to be almost the opposite of Zatopeks. Clarke said he rarely did training other than aerobic and when he did it was never more than once a week.
Apparently it was 10-100 meter surges with 100 meter recoveries.
I think Clarke ran 10-12 miles five evenings a week and probably did a lot of that at 5 minutes a mile or thereabouts. Five AM jogs of 4-5 miles and a long run in the hills on Sunday with the lads. I've read that there was a 17 mile route and a 21 mile route, but I have also read that he often ran for 40 klicks on Sunday. Saturdays are more vague, but he often raced on that day.
The number of races Clarke entered was phenomenal in today's terms and certainly would explain why he was no interval training advocate.
I may totally misunderstand your meaning of neural training. If not, the races Clarke ran would seem to tune his neural situation nicely.