On the left is a unmodified NAPA brand quad shock, and a 1/2" female spherical rod-end.
In the middle is the same shock with the top cut off and the shaft threaded with a 1/2" fine thread die. Enough length of shaft is cut off so that the rod-end hits the shock body when fully compressed. Your quad shock will need to have a 1/2" diameter shaft. The rod-end is also cut down.
On the right is a modified quad shock with rod-end attached. The new compressed length is 10 3/4". A jam nut is used instead of a regular nut. Because the jam nut is thinner, the compressed length of the shock is shorter.
1/2" Fine Thread Die
Hack Saw (18T works good)
Metal File or Bench Grinder
The file or bench grinder is used to flatten out the rod-end after cutting it with a hack saw, unless of course you are good at cutting straight. The cutting oil is used when threading the shaft. The shaft cuts easily with a hacksaw.