GottliebĀ® pop bumper (jet bumper, thumper bumper) ring and rod assembly has longer rod than standard.
The longer shafts accommodate the pop bumper spacer pad B-16632.
Reference:
Use A-4754 as a replacement
A-16634 ring and rod assembly for Gottlieb
B-16632 pop bumper spacer pad
A-17906 pop bumper coil bracket