Found it! If anyone cares. It's in the 1973 Runner's World "Finnish Running Secrets" book. I got the details wrong but the big picture right. It was the summer before Munich and of course training was pointing toward a peak at the games. All summer Viren had been racing (see malmo's statistics) and doing poorly in the pre-Olympics Viren tradition. The Finnish Association was hinting that only Vaatainen would be sent to the games (Vasala, another Lydiardite, also had yet to peak). The decisive trial was a match against GB and Spain six weeks before Munich. For nine days prior, Viren only jogged. Not clear how much but it could still have been high mileage (malmo says 349 miles in July). Viren ran 13:19, third all-time behind Clarke and Bedford. Two days later he did 7:43.2 for a new 11-second national record. I guess the take-home is that the usual wisdom of decreasing volume but maintaining intensity isn't necessarily the only answer. I'm going to try this.