They state:
Additional Custom Shaft Offerings at No Upcharge
Fujikura Motore Speeder 765
Mitsubishi Bassara 42
Mitsubishi Bassara 52
Matrix Ozik White Tie 50
Matrix Ozik Red Tie 60
Matrix 75M4 Black Tie
Project X LZ 6.0
Fubuki ZT 60
Fubuki Z 50
Aldila Tour GreenAldila Rogue*
Trevor, I see the same list you have listed here. My guess is that the shaft you are selecting that is a $300 upgrade is the Project X LZ Handmade, which is not the same as the Project X LZ. The regular Project X LZ is the stock shaft in the new XR line, and while I see it on the list in the 815 description, I do not see it available on the list when you start building yet.