J.E. Daniels posts a 1986 Starlog interview with Mel Blanc, along with a few comments from Friz Freleng. You can't always believe Blanc's stories, nor his evaluations of people he worked with, but it's still an interesting read.
One thing I hadn't quite caught before was that unlike today's voice actors, who tend to prefer recording radio-style with other actors, Blanc disliked that method of recording a cartoon because it took longer. So the way he tells it, he eventually switched over to just recording each character separately. Or at least, he was doing this by the time the cartoon studio was winding down, because you can hear him doing it on the '60s recording-session excerpts on the Looney Tunes Golden Collections, where he announces which character he's doing and then does a few takes of each line.