First if you wish to eliminate the separation charge from an estes engine just use a flat bladed screwdriver and scrape away the first layer on the end opposite the nozzle, it is very easy you will notice a distinct layer under the black powder of the charge.
Second I used the clip from the Jetex motor mount and had to wind masking tape around the estes motor to get a tight fit in the clip. If you use a V-tail the thrust stream will go between them if it flies straight. I did my trimming with a spent motor BTW.