Alpha measures the average excess return generated by a portfolio relative to its appropriate benchmark carrying a comparable risk profile. In this case, we have a large-cap portfolio that can be most appropriately benchmarked against the benchmark (LC).

As per the given data, the information ratio is the best fit for the calculation of excess return per unit of excess risk. First, we need to find the alpha, which can be calculated as below:

$$\text{Alpha} = \text{Annual portfolio return} - \text{Annual benchmark return}$$ $$= 12\% - 8\% = 4\%$$

Excess Return = Alpha = 4%

Now, we can calculate the information ratio:

$$\text{IR} = \frac{\alpha}{\text{TE}} = \frac{4\%}{6\%} = 0.67$$

An information ratio of 0.67 indicated that the manager earned 67 basis points of excess return per unit of excess risk.