The Halifax-based Americana band’s Past Lives album is a sonic trip down Route 66. It was the twilight of COVID-19 lockdowns in Nova Scotia, and Keith Maddison and Jeff Mosher were doing what lifelong rock ‘n’ rollers do: Playing some tunes. The two veterans of Halifax’s music scene—the former, a frontman for Maddison Avenue; the latter, a lead singer and saxophonist with The Mellotones—were at Maddison’s home “in the woods” of Fall River, chatting about days gone by…