Small chainring differences of 3-5 teeth were par for the course until the seventies, when 53/39 became dominant.

I still ride with half step (4 teeth difference) + granny on my touring bike, so I know assure you that it'll work. However, with narrow chains you want to be sure that the tops of the inner ring's teeth are below the shoulder on the inside of the outer ring. This is to ensure that the chain can't be trapped in the wider space between the rings.