Earlier, wrote:

Looking over the available illustrations on the net it appears
that the typical radial aircraft engine had a stroke longer
than the bore (undersquare). Is that right? ...

I think that most radials have bore to stroke ratios in line with
similar engines of other configuration. However, they often have
fairly long connecting rods (which is independent of stroke), which
tends to visually exaggerate the stroke.

Thanks, Bob K.