The R13 is pretty rare
Runder didn't core so the R13 is pretty heavy
Evan Clark cored everything so ebony makes more sense for his stuff
I haven't seen a lot of them for sale
Just a maple dowel or any hardwood
The extension system I use is basically the same thing as Cue fits except they are made in the USA buy the guy who designed it
That would allow you to be able to tap a 3/8 16 hole and depending on the distance you can use either the bumper with the long...
I think I would plug the 3/4 in and retap it for an extension bumper
If you do that then I can show you what bumper and extension I would recommend
I studied this extension thing for quite a while
I don't recommend the predator type QR extension for this application