I have a Jones and Shipman 520 and I was approached by a new member who had seen my posts on it asking for some dimensions for a part. My better half and I have been caught up in the Optus thing, so we are a little wary about sending things to unknown emails at the moment.
Instead, I'll post some drawings and photos here.
The pawl flicks into a groove on the feed wheel; there is a two position ball detent that holds it. The photo shows the out position. In the in position, the end engages with a stop in the groove on the wheel
DSCN9008.JPG
The ball is 3/16" diameter, the spring is 3/8" long, 5/32" OD and is 5 turns of 0.020" wire. Nothing critical there - it just holds the ball in a dimple on the body casting.
DSCN9013.JPG DSCN9011.JPG DSCN9010.JPG
The two most complex parts are the shoulder screw and pawl, drawn below.
Grinder pawl.jpg

Michael