I'm guessing the two non-reference conductors are the same physically, as you just have the one value each of C and L. Also, the resistance seems a bit high, you might want to check this (do you mean conductance?)
Use the above data to form (complex) matrices [Z] = [R] + jω[L] and [Y] = jω[C], where
The terminal phase velocities are then given by the full matrix ([Z]*[Y])^(1/2). Taking the eigenmodes of this matrix gives the modal phase velocities - these are the two that you want.