I have tried to put optios to the weapons being low level and it does not allow me to put (special soul crystal) when it can be placed 1 normal and 1 special. I do not know if it's a restriction, but I will not allow it. Should allow it since if in the description of the weapon comes out that you can, 1 normal and 1 special.
Try these two items:
GREAT PATA and SAMURAI LONG SWORD "both grade C"