I wanted to use the prop adapter and there is a significant modification required to do that. The instructions do not explain this in words or pictures. Horizon chat offered me a link to a forum thread that had the procedure. Thanks for that! Here it is: https://www.rcgroups.com/forums/showthread.php?692680-Installing-prop-adapter-collett-on-E-Flite-Park-300

"Remove the snap ring from the back side of the motor, loosen the set screw from the front of the motor, and push the shaft out the front. You can then mount the collet-style prop adapter on the exposed motor shaft."

The shaft does not slide easily through the motor. I had to make a jig on my vice and tap the shaft through with a peen hammer. This made me nervous! It turned out fine and the collet slides on the now protruding shaft from the front instead of the back. There is an alternate location for the snap ring to go back on the end of the shaft.
Also the snap ring is not easy to get off. watch out it'll fly away. It also bends easily. I wish they included a spare ring with the parts (and explained how to do this).

It bench tests fine now and I look forward to putting it on my plane. I hope this info helps someone else that does not know. I learned a lot.

Very good motor. It gets the thrust I need and is very small and compact.

Pass the test I have my Park 300 in a Funtana 300 I will fly ,fly and fly then put in a new battery then fly ,fly fly,some more I am pushing hard and still going stong.