Spark Plug technology has progressed a long way since the 1940's, if those AC 44 plugs are old stock or not of a modern type then NGK will give better performance. I think NGK were the first to use a copper core, others followed, this and other features, gave a wider heat range, giving better performance. Sometimes an old engine oils plugs so you go for a hotter grade, next number up, etc., with these modern plugs the heat ranges tend to overlap adjacent grades. In my Bedford, I use Champion J8C, which is a copper core, denoted by the C suffix. They have been in there for years and still good.