Not true. The breakerless caps are significantly larger. It is true that an adapter ring was used since the aluminum distributor housing is basically unchanged. See image below.
IMG_1292.jpg
I'm in the middle of gathering parts for a duraspark swap on my '66 Mustang. The cap on the left is form the duraspark distributor from a '77 302 Mustang that I plan on using. The cap on the right is the original Ford points cap. Notice the size difference.