Yep Al's store sells a Owl gut. I think it takes a half inch bore. For your exhaust end I bore 1/2" and then the last 1/4" I use a 1/4" bit. When making a owl call with a reed set you have build back pressure to get the right sound. Make your insert short like 2". I like to use Wades gutsert for them. JC products also makes a tone board.
Larry