For illustration purposes and education on this lost style of bowling, I have just uploaded a slow motion video showing how the classic Full Roller release is executed.
You can see that the ball is held in a suitcase grip and at the moment of release the thumb is exiting just a fraction of a second prior to the fingers.
The thumb and fingers almost come out at the same moment.
You can also note that the ball has a 90 degree axis rotation with zero tilt.
The ball actually goes very straight up the lane, holding the line up the track, which seems counter intuitive considering it has a 90 degree rotation.
Technically a 90 degree axis rotation has the longest skid phase and potentially the greatest hook angle.
However, my Full Roller release specs have a lower rev rate and this allows my ball to get great length and actually hook very mildly giving me a lot of control of the pocket with the right ball.
By the time the ball reaches the backend you can see that it has shed all its side roll and has turned towards the pins in a forward roll with the thumbhole on the right side and the finger holes on the left side as the ball tracks/rolls between them. The ball used in this video is my Billy Hardwick rubber ball.