Years before Pink Floyd bassist Roger Waters would say he came to “regret” one of the band’s most distinctive cuts, guitarist David Gilmour went so far as to refuse to sing it in the first place.

At 5:55 p.m. on a Friday evening in Gloucester, England, David Purchase was still singing — 41 hours and 55 minutes after he had begun. His voice was hoarse, his legs felt unsteady, and his eyes ached ...