Being that I am from that era (I was a little kid in 63) . . . Yes, it was very commonly done for two reasons. Mostly for folks who lived on dirt roads to help protect the rad from possible punctures from rocks kicked up by passing cars. People also did this to help keep bugs from getting imbedded in the rad fins which are hard to get out – a dry brush would easily brush them off screening as they get quite dried out in that hot spot.