Replace O-ring, stand connector on end and drop the parts in.  Use a hammer to tap them in.  Done.

Use a hammer to tap the bushing and stuff out of the connector body.  It will catch the parts so you don't have to crawl around on the floor looking for them.

Place fuel connector on fixture and eye-ball align it with the cavities.  Insert driver pin into hose nipple.

To Use, remove the driver pin from the stowage slot and run the screw down below the surface.

It is best to grab the fixture in a vise, or at least lay it on something hard and heavy such as a brick or even a concrete floor if you must.  It won't work well on a bouncy bench top

This fixture makes it easy to dis-assemble and re-assemble the OMC dual hose (pressure tank) fuel connector for repair or to replace the O-rings.  Trying to pick those O-rings out without taking it apart is difficult at best, and impossible if they are 50 years old and petrified.  Not only that, you probably will scratch the inside of the brass retainer, possibly causing a permanent leak.