In the How To section there should be a chart giving shaft sizes.
I'm not sure how critical length is but I use an inch.I chucked the piece in a drill press and used my broadhead file to bevel the rear edge.Someone talked about using a reloader's case trimmer for that.
Lightly sand the end of the shaft and install with a good epoxy.If your aluminum shaft section is to narrow to slide over the lip of your insert,you may have to install the aluminum section first,then the insert.
While you are at it,take the time to put a small,1/4"-1/2" piece on the nock end of the shaft.